diff --git a/changelog_entry.yaml b/changelog_entry.yaml
index e69de29bb2d..b12a0a80aad 100644
--- a/changelog_entry.yaml
+++ b/changelog_entry.yaml
@@ -0,0 +1,4 @@
+- bump: minor
+  changes:
+    added:
+      - Illinois I-PASS Assist program eligibility.
diff --git a/policyengine_us/parameters/gov/states/il/tollway/ipass_assist/eligibility/fpg_limit.yaml b/policyengine_us/parameters/gov/states/il/tollway/ipass_assist/eligibility/fpg_limit.yaml
new file mode 100644
index 00000000000..fc98f557557
--- /dev/null
+++ b/policyengine_us/parameters/gov/states/il/tollway/ipass_assist/eligibility/fpg_limit.yaml
@@ -0,0 +1,13 @@
+description: Illinois limits income to this share of the federal poverty level under the I-PASS Assist program.
+values:
+  2021-01-01: 2.5
+
+metadata:
+  unit: /1
+  period: year
+  label: Illinois I-PASS Assist income limit as share of FPL
+  reference:
+    - title: Illinois Tollway I-PASS Assist - 250% of Federal Poverty Guidelines
+      href: https://agency.illinoistollway.com/assist
+    - title: Illinois Tollway Expansion Announcement (June 2021) - 250% FPG threshold
+      href: https://agency.illinoistollway.com/-/illinois-tollway-significantly-expands-i-pass-assist-program-1
diff --git a/policyengine_us/tests/policy/baseline/gov/states/il/tollway/ipass_assist/il_ipass_assist_categorical_eligible.yaml b/policyengine_us/tests/policy/baseline/gov/states/il/tollway/ipass_assist/il_ipass_assist_categorical_eligible.yaml
new file mode 100644
index 00000000000..88d02b0a1df
--- /dev/null
+++ b/policyengine_us/tests/policy/baseline/gov/states/il/tollway/ipass_assist/il_ipass_assist_categorical_eligible.yaml
@@ -0,0 +1,20 @@
+# Illinois I-PASS Assist categorical eligibility tests
+# Formula: snap > 0
+#
+# Source: https://www.dhs.state.il.us/page.aspx?item=150431
+
+- name: Case 1, has SNAP.
+  period: 2025
+  input:
+    state_code: IL
+    snap: 1
+  output:
+    il_ipass_assist_categorical_eligible: true
+
+- name: Case 2, no SNAP.
+  period: 2025
+  input:
+    state_code: IL
+    snap: 0
+  output:
+    il_ipass_assist_categorical_eligible: false
diff --git a/policyengine_us/tests/policy/baseline/gov/states/il/tollway/ipass_assist/il_ipass_assist_eligible.yaml b/policyengine_us/tests/policy/baseline/gov/states/il/tollway/ipass_assist/il_ipass_assist_eligible.yaml
new file mode 100644
index 00000000000..6f724269def
--- /dev/null
+++ b/policyengine_us/tests/policy/baseline/gov/states/il/tollway/ipass_assist/il_ipass_assist_eligible.yaml
@@ -0,0 +1,49 @@
+# Illinois I-PASS Assist eligibility unit tests
+# Formula: (income_eligible | categorical_eligible) with defined_for = StateCode.IL
+#
+# Source: https://agency.illinoistollway.com/assist
+
+- name: Case 1, income eligible only.
+  period: 2025
+  input:
+    state_code: IL
+    il_ipass_assist_income_eligible: true
+    il_ipass_assist_categorical_eligible: false
+  output:
+    il_ipass_assist_eligible: true
+
+- name: Case 2, categorical eligible only.
+  period: 2025
+  input:
+    state_code: IL
+    il_ipass_assist_income_eligible: false
+    il_ipass_assist_categorical_eligible: true
+  output:
+    il_ipass_assist_eligible: true
+
+- name: Case 3, both pathways.
+  period: 2025
+  input:
+    state_code: IL
+    il_ipass_assist_income_eligible: true
+    il_ipass_assist_categorical_eligible: true
+  output:
+    il_ipass_assist_eligible: true
+
+- name: Case 4, neither pathway.
+  period: 2025
+  input:
+    state_code: IL
+    il_ipass_assist_income_eligible: false
+    il_ipass_assist_categorical_eligible: false
+  output:
+    il_ipass_assist_eligible: false
+
+- name: Case 5, non-IL resident.
+  period: 2025
+  input:
+    state_code: WI
+    il_ipass_assist_income_eligible: true
+    il_ipass_assist_categorical_eligible: true
+  output:
+    il_ipass_assist_eligible: false
diff --git a/policyengine_us/tests/policy/baseline/gov/states/il/tollway/ipass_assist/il_ipass_assist_income_eligible.yaml b/policyengine_us/tests/policy/baseline/gov/states/il/tollway/ipass_assist/il_ipass_assist_income_eligible.yaml
new file mode 100644
index 00000000000..ba59907a159
--- /dev/null
+++ b/policyengine_us/tests/policy/baseline/gov/states/il/tollway/ipass_assist/il_ipass_assist_income_eligible.yaml
@@ -0,0 +1,302 @@
+# Illinois I-PASS Assist income eligibility tests
+# Income limit: 250% of Federal Poverty Guidelines
+#
+# 2025 FPL for contiguous US (Illinois):
+# - 1 person: $15,650 * 2.5 = $39,125
+# - 2 person: $21,150 * 2.5 = $52,875
+# - 3 person: $26,650 * 2.5 = $66,625
+# - 4 person: $32,150 * 2.5 = $80,375
+# - 8 person: $48,650 * 2.5 = $121,625
+#
+# Source: https://agency.illinoistollway.com/assist
+
+- name: Case 1, single person below 250% FPL.
+  period: 2025-01
+  input:
+    state_code: IL
+    employment_income: 36_000  # $36,000/year < $39,125 limit
+  output:
+    il_ipass_assist_income_eligible: true
+
+- name: Case 2, single person above 250% FPL.
+  period: 2025-01
+  input:
+    state_code: IL
+    employment_income: 48_000  # $48,000/year > $39,125 limit
+  output:
+    il_ipass_assist_income_eligible: false
+
+- name: Case 3, single person at exactly 250% FPL.
+  period: 2025-01
+  input:
+    state_code: IL
+    employment_income: 39_125  # Exactly at 250% FPL for 1 person
+  output:
+    il_ipass_assist_income_eligible: true
+
+- name: Case 4, family of 4 below 250% FPL.
+  period: 2025-01
+  input:
+    people:
+      person1:
+        age: 35
+        employment_income: 48_000
+      person2:
+        age: 32
+        employment_income: 24_000
+      person3:
+        age: 10
+      person4:
+        age: 7
+    spm_units:
+      spm_unit:
+        members: [person1, person2, person3, person4]
+    households:
+      household:
+        members: [person1, person2, person3, person4]
+        state_code: IL
+  output:
+    # Total income: $72,000/year < $80,375 limit for 4-person household
+    il_ipass_assist_income_eligible: true
+
+- name: Case 5, family of 4 above 250% FPL.
+  period: 2025-01
+  input:
+    people:
+      person1:
+        age: 40
+        employment_income: 60_000
+      person2:
+        age: 38
+        employment_income: 30_000
+      person3:
+        age: 12
+      person4:
+        age: 8
+    spm_units:
+      spm_unit:
+        members: [person1, person2, person3, person4]
+    households:
+      household:
+        members: [person1, person2, person3, person4]
+        state_code: IL
+  output:
+    # Total income: $90,000/year > $80,375 limit for 4-person household
+    il_ipass_assist_income_eligible: false
+
+- name: Case 6, two-person household just below threshold.
+  period: 2025-01
+  input:
+    people:
+      person1:
+        age: 45
+        employment_income: 50_000
+      person2:
+        age: 42
+    spm_units:
+      spm_unit:
+        members: [person1, person2]
+    households:
+      household:
+        members: [person1, person2]
+        state_code: IL
+  output:
+    # Total income: $50,000/year < $52,875 limit for 2-person household
+    il_ipass_assist_income_eligible: true
+
+# ============================================================================
+# EDGE CASE TESTS
+# ============================================================================
+
+- name: Case 7, boundary one dollar above threshold.
+  # Tests that <= operator works correctly (at threshold+1 should fail)
+  period: 2025-01
+  input:
+    state_code: IL
+    employment_income: 39_126  # $39,125 + 1 = one dollar above 250% FPL
+  output:
+    # Threshold: $15,650 * 2.5 = $39,125
+    # Income $39,126 > $39,125 -> NOT eligible
+    il_ipass_assist_income_eligible: false
+
+- name: Case 8, zero income household.
+  # Tests minimum bound - should always be eligible
+  period: 2025-01
+  input:
+    state_code: IL
+    employment_income: 0
+  output:
+    # $0 <= $39,125 -> eligible
+    il_ipass_assist_income_eligible: true
+
+- name: Case 9, very large household 8 members at threshold.
+  # Tests FPG scaling with large household at exact boundary
+  # 2025 FPL for 8 people: $15,650 + 7 * $5,500 = $54,150
+  # 250% FPL = $54,150 * 2.5 = $135,375
+  period: 2025-01
+  input:
+    people:
+      person1:
+        age: 45
+        employment_income: 75_000
+      person2:
+        age: 43
+        employment_income: 60_375  # Total = $135,375 (exactly at threshold)
+      person3:
+        age: 20
+      person4:
+        age: 18
+      person5:
+        age: 15
+      person6:
+        age: 12
+      person7:
+        age: 8
+      person8:
+        age: 5
+    spm_units:
+      spm_unit:
+        members: [person1, person2, person3, person4, person5, person6, person7, person8]
+    households:
+      household:
+        members: [person1, person2, person3, person4, person5, person6, person7, person8]
+        state_code: IL
+  output:
+    # 8-person 250% FPL = $135,375
+    # Total income: $75,000 + $60,375 = $135,375 (exactly at threshold)
+    il_ipass_assist_income_eligible: true
+
+- name: Case 10, very large household one dollar over.
+  # Tests boundary for large household
+  # 2025 FPL for 8 people: $15,650 + 7 * $5,500 = $54,150
+  # 250% FPL = $54,150 * 2.5 = $135,375
+  period: 2025-01
+  input:
+    people:
+      person1:
+        age: 45
+        employment_income: 75_000
+      person2:
+        age: 43
+        employment_income: 60_376  # Total = $135,376 (one dollar over)
+      person3:
+        age: 20
+      person4:
+        age: 18
+      person5:
+        age: 15
+      person6:
+        age: 12
+      person7:
+        age: 8
+      person8:
+        age: 5
+    spm_units:
+      spm_unit:
+        members: [person1, person2, person3, person4, person5, person6, person7, person8]
+    households:
+      household:
+        members: [person1, person2, person3, person4, person5, person6, person7, person8]
+        state_code: IL
+  output:
+    # 8-person 250% FPL = $135,375
+    # Total income: $75,000 + $60,376 = $135,376 > $135,375
+    il_ipass_assist_income_eligible: false
+
+- name: Case 11, single person with non-employment income.
+  # Tests that net income includes various sources
+  period: 2025-01
+  input:
+    people:
+      person1:
+        age: 68
+        social_security: 24_000
+        interest_income: 5_000
+    spm_units:
+      spm_unit:
+        members: [person1]
+    households:
+      household:
+        members: [person1]
+        state_code: IL
+  output:
+    # Total income: $24,000 + $5,000 = $29,000
+    # 250% FPL for 1 person: $39,125
+    # $29,000 < $39,125 -> eligible
+    il_ipass_assist_income_eligible: true
+
+- name: Case 12, two-person at exact threshold.
+  # Tests boundary for 2-person household
+  period: 2025-01
+  input:
+    people:
+      person1:
+        age: 55
+        employment_income: 52_875  # Exactly at 2-person 250% FPL
+      person2:
+        age: 52
+    spm_units:
+      spm_unit:
+        members: [person1, person2]
+    households:
+      household:
+        members: [person1, person2]
+        state_code: IL
+  output:
+    # 2-person 250% FPL = $21,150 * 2.5 = $52,875
+    # Income $52,875 <= $52,875 -> eligible
+    il_ipass_assist_income_eligible: true
+
+- name: Case 13, two-person one dollar above threshold.
+  period: 2025-01
+  input:
+    people:
+      person1:
+        age: 55
+        employment_income: 52_876  # One dollar above 2-person 250% FPL
+      person2:
+        age: 52
+    spm_units:
+      spm_unit:
+        members: [person1, person2]
+    households:
+      household:
+        members: [person1, person2]
+        state_code: IL
+  output:
+    # 2-person 250% FPL = $52,875
+    # Income $52,876 > $52,875 -> NOT eligible
+    il_ipass_assist_income_eligible: false
+
+- name: Case 14, extremely high income.
+  # Tests behavior with very large income values
+  period: 2025-01
+  input:
+    state_code: IL
+    employment_income: 1_000_000  # $1 million income
+  output:
+    # Obviously above 250% FPL ($39,125)
+    il_ipass_assist_income_eligible: false
+
+- name: Case 15, three-person at exact threshold.
+  period: 2025-01
+  input:
+    people:
+      person1:
+        age: 40
+        employment_income: 66_625  # Exactly at 3-person 250% FPL
+      person2:
+        age: 38
+      person3:
+        age: 10
+    spm_units:
+      spm_unit:
+        members: [person1, person2, person3]
+    households:
+      household:
+        members: [person1, person2, person3]
+        state_code: IL
+  output:
+    # 3-person 250% FPL = $26,650 * 2.5 = $66,625
+    # Income $66,625 <= $66,625 -> eligible
+    il_ipass_assist_income_eligible: true
diff --git a/policyengine_us/tests/policy/baseline/gov/states/il/tollway/ipass_assist/integration.yaml b/policyengine_us/tests/policy/baseline/gov/states/il/tollway/ipass_assist/integration.yaml
new file mode 100644
index 00000000000..5b51e11212c
--- /dev/null
+++ b/policyengine_us/tests/policy/baseline/gov/states/il/tollway/ipass_assist/integration.yaml
@@ -0,0 +1,80 @@
+# Illinois I-PASS Assist integration tests
+# End-to-end scenarios testing full calculation chain
+#
+# Eligibility: IL resident AND (income <= 250% FPL OR SNAP recipient)
+#
+# Source: https://agency.illinoistollway.com/assist
+
+- name: Case 1, moderate income worker eligible via income.
+  period: 2025
+  input:
+    state_code: IL
+    employment_income: 35_000
+  output:
+    # 1-person 250% FPL = $39,125
+    # $35,000 < $39,125 -> income eligible
+    # $35,000 > SNAP limit -> no SNAP
+    il_ipass_assist_income_eligible: true
+    il_ipass_assist_categorical_eligible: false
+    il_ipass_assist_eligible: true
+
+- name: Case 2, low income family eligible via both pathways.
+  period: 2025
+  input:
+    people:
+      person1:
+        age: 32
+        employment_income: 24_000
+      person2:
+        age: 30
+      person3:
+        age: 8
+      person4:
+        age: 5
+    spm_units:
+      spm_unit:
+        members: [person1, person2, person3, person4]
+    households:
+      household:
+        members: [person1, person2, person3, person4]
+        state_code: IL
+  output:
+    # 4-person 250% FPL = $80,375
+    # $24,000 < $80,375 -> income eligible
+    # $24,000 < SNAP limit -> gets SNAP -> categorical eligible
+    il_ipass_assist_income_eligible: true
+    il_ipass_assist_categorical_eligible: true
+    il_ipass_assist_eligible: true
+
+- name: Case 3, high income not eligible.
+  period: 2025
+  input:
+    people:
+      person1:
+        age: 45
+        employment_income: 60_000
+      person2:
+        age: 42
+        employment_income: 40_000
+    spm_units:
+      spm_unit:
+        members: [person1, person2]
+    households:
+      household:
+        members: [person1, person2]
+        state_code: IL
+  output:
+    # 2-person 250% FPL = $52,875
+    # $100,000 > $52,875 -> NOT income eligible
+    # $100,000 > SNAP limit -> no SNAP
+    il_ipass_assist_income_eligible: false
+    il_ipass_assist_categorical_eligible: false
+    il_ipass_assist_eligible: false
+
+- name: Case 4, non-IL resident not eligible.
+  period: 2025
+  input:
+    state_code: WI
+    employment_income: 20_000
+  output:
+    il_ipass_assist_eligible: false
diff --git a/policyengine_us/variables/gov/states/il/tollway/ipass_assist/il_ipass_assist_categorical_eligible.py b/policyengine_us/variables/gov/states/il/tollway/ipass_assist/il_ipass_assist_categorical_eligible.py
new file mode 100644
index 00000000000..2054c40e370
--- /dev/null
+++ b/policyengine_us/variables/gov/states/il/tollway/ipass_assist/il_ipass_assist_categorical_eligible.py
@@ -0,0 +1,17 @@
+from policyengine_us.model_api import *
+
+
+class il_ipass_assist_categorical_eligible(Variable):
+    value_type = bool
+    entity = SPMUnit
+    definition_period = YEAR
+    label = "Illinois I-PASS Assist categorically eligible"
+    reference = [
+        "https://agency.illinoistollway.com/assist",
+        "https://www.dhs.state.il.us/page.aspx?item=150431",
+    ]
+    defined_for = StateCode.IL
+
+    def formula(spm_unit, period, parameters):
+        # Per IL DHS: "Customers getting SNAP may be eligible for I-PASS Assist"
+        return spm_unit("snap", period) > 0
diff --git a/policyengine_us/variables/gov/states/il/tollway/ipass_assist/il_ipass_assist_eligible.py b/policyengine_us/variables/gov/states/il/tollway/ipass_assist/il_ipass_assist_eligible.py
new file mode 100644
index 00000000000..31d95da76e1
--- /dev/null
+++ b/policyengine_us/variables/gov/states/il/tollway/ipass_assist/il_ipass_assist_eligible.py
@@ -0,0 +1,20 @@
+from policyengine_us.model_api import *
+
+
+class il_ipass_assist_eligible(Variable):
+    value_type = bool
+    entity = SPMUnit
+    definition_period = YEAR
+    label = "Illinois I-PASS Assist eligible"
+    reference = [
+        "https://agency.illinoistollway.com/assist",
+        "https://www.dhs.state.il.us/page.aspx?item=150431",
+    ]
+    defined_for = StateCode.IL
+
+    def formula(spm_unit, period, parameters):
+        income_eligible = spm_unit("il_ipass_assist_income_eligible", period)
+        categorical_eligible = spm_unit(
+            "il_ipass_assist_categorical_eligible", period
+        )
+        return income_eligible | categorical_eligible
diff --git a/policyengine_us/variables/gov/states/il/tollway/ipass_assist/il_ipass_assist_income_eligible.py b/policyengine_us/variables/gov/states/il/tollway/ipass_assist/il_ipass_assist_income_eligible.py
new file mode 100644
index 00000000000..60b27458568
--- /dev/null
+++ b/policyengine_us/variables/gov/states/il/tollway/ipass_assist/il_ipass_assist_income_eligible.py
@@ -0,0 +1,20 @@
+from policyengine_us.model_api import *
+
+
+class il_ipass_assist_income_eligible(Variable):
+    value_type = bool
+    entity = SPMUnit
+    definition_period = YEAR
+    label = "Illinois I-PASS Assist income eligible"
+    reference = [
+        "https://agency.illinoistollway.com/assist",
+        "https://www.dhs.state.il.us/page.aspx?item=150431",
+    ]
+    defined_for = StateCode.IL
+
+    def formula(spm_unit, period, parameters):
+        p = parameters(period).gov.states.il.tollway.ipass_assist.eligibility
+        fpg = spm_unit("spm_unit_fpg", period)
+        # Income verified by Illinois Department of Revenue
+        gross_income = add(spm_unit, period, ["irs_gross_income"])
+        return gross_income <= fpg * p.fpg_limit