Medicare Advantage in Marin County, California
29,558 people in Marin County, California were enrolled in Medicare Advantage in October 2026, 45.3% of 65,281 eligible beneficiaries (−1.1 pts since October 2025). Kaiser Foundation Health Plan, Inc. is the largest parent organization with 81% of reported enrollment; 12 parent organizations have 11 or more members and the HHI is 6,610 (highly concentrated). HRSA classifies the county as partly rural. For 2027, 169 members here are in plans that terminate or leave the county. MA plans offered go from 12 to 11.
Parent organizations in Marin County
| Parent organization | Members | Change since October 2025 | Share |
|---|---|---|---|
| Kaiser Foundation Health Plan, Inc. | 23,827 | +564 | 80.8% |
| Alignment Healthcare USA, LLC | 1,863 | +971 | 6.3% |
| California Physicians' Service | 1,173 | +28 | 4.0% |
| UnitedHealth Group, Inc. | 1,120 | −1,370 | 3.8% |
| Humana Inc. | 524 | −66 | 1.8% |
| Elevance Health, Inc. | 461 | +249 | 1.6% |
| Imperial Health Plan of California | 221 | +185 | 0.7% |
| CVS Health Corporation | 218 | −744 | 0.7% |
| Blue Cross Blue Shield of Michigan Mutual Ins. Co. | 32 | −1 | 0.1% |
| Health Care Service Corporation | 14 | +1 | under 0.1% |
| SCAN Group | 14 | new | under 0.1% |
| Curana Health Holdings, LLC | 11 | new | under 0.1% |
CMS suppresses county and contract counts of 10 or fewer; shares are of reported enrollment.
Value-based care alongside MA
In PY 2024, 1,764 beneficiaries in Marin County were assigned to 128 Medicare Shared Savings Program ACOs, 7.2% of assignable Original Medicare beneficiaries. Together, roughly 49% of all Medicare beneficiaries in the county are in Medicare Advantage or an MSSP ACO. See the ACOs in the MSSP Explorer.