Medicare Advantage in King County, Washington
198,653 people in King County, Washington were enrolled in Medicare Advantage in October 2026, 53.7% of 370,069 eligible beneficiaries (−0.7 pts since October 2025). UnitedHealth Group, Inc. is the largest parent organization with 44% of reported enrollment; 18 parent organizations have 11 or more members and the HHI is 2,775 (highly concentrated). HRSA classifies the county as partly rural. For 2027, 26,215 members here are in plans that terminate or leave the county. MA plans offered go from 37 to 30.
Parent organizations in King County
| Parent organization | Members | Change since October 2025 | Share |
|---|---|---|---|
| UnitedHealth Group, Inc. | 87,307 | +1,498 | 44.0% |
| Humana Inc. | 38,280 | +5,033 | 19.3% |
| Kaiser Foundation Health Plan, Inc. | 31,301 | −779 | 15.8% |
| CVS Health Corporation | 28,369 | −2,176 | 14.3% |
| Cambia Health Solutions, Inc. | 4,742 | −453 | 2.4% |
| Molina Healthcare, Inc. | 2,787 | +165 | 1.4% |
| Centene Corporation | 1,747 | +29 | 0.9% |
| Community Health Plan of Washington | 1,706 | −819 | 0.9% |
| Providence Health & Services | 877 | +66 | 0.4% |
| Elevance Health, Inc. | 665 | −47 | 0.3% |
| Blue Cross Blue Shield of Michigan Mutual Ins. Co. | 140 | −12 | under 0.1% |
| International Community Health Services | 129 | +20 | under 0.1% |
| California Physicians' Service | 68 | +9 | under 0.1% |
| Health Care Service Corporation | 59 | −2 | under 0.1% |
| MultiCare Health Systems | 40 | +12 | 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, 62,395 beneficiaries in King County were assigned to 264 Medicare Shared Savings Program ACOs, 61.6% of assignable Original Medicare beneficiaries. Together, roughly 82% of all Medicare beneficiaries in the county are in Medicare Advantage or an MSSP ACO. See the ACOs in the MSSP Explorer.