Medicare Advantage in San Mateo County, California
73,795 people in San Mateo County, California were enrolled in Medicare Advantage in October 2026, 50.7% of 145,668 eligible beneficiaries (+0.1 pts since October 2025). Kaiser Foundation Health Plan, Inc. is the largest parent organization with 59% of reported enrollment; 17 parent organizations have 11 or more members and the HHI is 3,702 (highly concentrated). HRSA classifies the county as partly rural. For 2027, 4,189 members here are in plans that terminate or leave the county, and Molina Healthcare, Inc., SANTA CLARA COUNTY HEALTH AUTHORITY leave. MA plans offered go from 22 to 18.
Parent organizations in San Mateo County
| Parent organization | Members | Change since October 2025 | Share |
|---|---|---|---|
| Kaiser Foundation Health Plan, Inc. | 43,155 | +1,380 | 58.6% |
| Health Plan of San Mateo | 7,947 | +149 | 10.8% |
| Alignment Healthcare USA, LLC | 4,846 | +1,339 | 6.6% |
| UnitedHealth Group, Inc. | 4,333 | −325 | 5.9% |
| California Physicians' Service | 4,214 | −892 | 5.7% |
| SCAN Group | 3,352 | +1,663 | 4.6% |
| Elevance Health, Inc. | 2,211 | −142 | 3.0% |
| CVS Health Corporation | 1,376 | −418 | 1.9% |
| Molina Healthcare, Inc. | 1,013 | −798 | 1.4% |
| Chinese Hospital Association | 625 | −6 | 0.8% |
| Imperial Health Plan of California | 273 | +53 | 0.4% |
| Humana Inc. | 152 | +100 | 0.2% |
| Centene Corporation | 36 | −177 | under 0.1% |
| Blue Cross Blue Shield of Michigan Mutual Ins. Co. | 24 | 0 | under 0.1% |
| On Lok, Inc. | 13 | 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, 21,967 beneficiaries in San Mateo County were assigned to 117 Medicare Shared Savings Program ACOs, 51.4% of assignable Original Medicare beneficiaries. Together, roughly 76% of all Medicare beneficiaries in the county are in Medicare Advantage or an MSSP ACO. See the ACOs in the MSSP Explorer.