Medicare Advantage in Williamson County, Illinois
6,210 people in Williamson County, Illinois were enrolled in Medicare Advantage in October 2026, 38.0% of 16,330 eligible beneficiaries (+0.3 pts since October 2025). CVS Health Corporation is the largest parent organization with 54% of reported enrollment; 8 parent organizations have 11 or more members and the HHI is 3,321 (highly concentrated). HRSA classifies the county as fully rural. For 2027, 1,522 members here are in plans that terminate or leave the county, and Health Care Service Corporation leaves. MA plans offered go from 14 to 5.
Parent organizations in Williamson County
| Parent organization | Members | Change since October 2025 | Share |
|---|---|---|---|
| CVS Health Corporation | 3,318 | +533 | 53.7% |
| Health Care Service Corporation | 851 | −668 | 13.8% |
| Humana Inc. | 581 | +125 | 9.4% |
| UMWA Health and Retirement Funds | 537 | −30 | 8.7% |
| Centene Corporation | 500 | +462 | 8.1% |
| Molina Healthcare, Inc. | 215 | −12 | 3.5% |
| UnitedHealth Group, Inc. | 163 | −38 | 2.6% |
| Elevance Health, Inc. | 15 | +1 | 0.2% |
CMS suppresses county and contract counts of 10 or fewer; shares are of reported enrollment.
Value-based care alongside MA
In PY 2024, 1,213 beneficiaries in Williamson County were assigned to 49 Medicare Shared Savings Program ACOs, 14.3% of assignable Original Medicare beneficiaries. Together, roughly 47% of all Medicare beneficiaries in the county are in Medicare Advantage or an MSSP ACO. See the ACOs in the MSSP Explorer.