2,407,750
Total Medicare beneficiaries
42.8%
On Medicare Advantage
57.2%
On Original Medicare
$202.90
Standard Part B premium (2026)
Medicare Enrollment by County in Illinois
The 15 most-populous counties by Medicare beneficiaries. Click any column heading to sort. Medicare Advantage percentage is the share of each county’s beneficiaries enrolled in an MA or other health plan.
| Cook County | 864,789 | 43.8% |
| Dupage County | 178,091 | 38.0% |
| Lake County | 129,192 | 33.4% |
| Will County | 118,472 | 41.4% |
| Kane County | 89,821 | 40.2% |
| Mchenry County | 62,883 | 35.7% |
| Winnebago County | 62,040 | 56.6% |
| Madison County | 58,734 | 53.5% |
| St. Clair County | 52,680 | 54.7% |
| Sangamon County | 44,173 | 56.5% |
| Peoria County | 37,559 | 49.4% |
| Champaign County | 32,428 | 58.4% |
| Rock Island County | 32,277 | 57.8% |
| Tazewell County | 30,541 | 43.5% |
| Mclean County | 29,649 | 44.2% |
Key Findings: Medicare in Illinois
- 1Illinois has 2,407,750 Medicare beneficiaries across 102 counties or county-equivalent areas in the CMS 2024 annual enrollment file.
- 242.8% of beneficiaries are enrolled in Medicare Advantage or other health plans, compared with 57.2% in Original Medicare.
- 3Cook County has the largest Medicare beneficiary population among the county rows shown here, with 864,789 beneficiaries.
- 4Medicare Advantage participation varies by county, so statewide percentages should not be treated as plan availability for a specific address.
- 5Plan availability, provider networks, drug formularies, premiums, and benefits should be verified for the beneficiary's ZIP code and current plan year.
How Illinois Compares to National Averages
Medicare Advantage penetration
Illinois is at 42.8%, 11.2 points below the national average of about 54%.
Plans available
Nationally, the average beneficiary can choose from about 32 Medicare Advantage prescription-drug plans for 2026. The exact number available depends on your county.
Medicare Supplement (Medigap)
Nationally, about 41.9% of Original Medicare beneficiaries carry a Medigap policy (AHIP, 2023). State-by-state Medigap rates are not published in an open dataset, so this figure is national. In Illinois, 57.2% of beneficiaries are in Original Medicare and therefore eligible to buy Medigap.
Explore Medicare by County in Illinois
Use the CMS-backed county enrollment data above as context, then verify current Medicare plan availability, networks, prescriptions, costs, and benefits for your exact ZIP code.
Browse Illinois County GuidesMethodology & Sources
Enrollment and county data: Centers for Medicare & Medicaid Services, Medicare Monthly Enrollment, 2024 (data.cms.gov). Figures are 2024 annual counts. Medicare Advantage percentage = (beneficiaries in Medicare Advantage & Other Health Plans ÷ total beneficiaries) × 100. The county table shows the 15 most-populous counties of 102 total.
Part B premium: CMS, 2026 Medicare Parts A & B Premiums and Deductibles. The standard premium is set federally and is the same in every state; higher-income beneficiaries pay an income-related adjustment (IRMAA).
Plan counts and Medigap: KFF, Medicare Advantage 2026 Spotlight (CMS Landscape files); AHIP, The State of Medicare Supplement Coverage, 2023. These are reported as national figures only.
Limitations: Medicare Supplement (Medigap) enrollment and per-county plan counts are not available in an open dataset at the state or county level, so they are not shown per county. Percentages are rounded. Last updated 2026-09-19.
This page is for educational purposes. HealthPlan Connect is not affiliated with or endorsed by CMS or any government agency. Contact a licensed advisor for current plan options in your area.