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Medicare Advantage, one county at a time.
For each county: how many Medicare-eligible people are in Medicare Advantage as of April 2026, which parent organizations hold the market and with what share, and what the CMS 2026 Landscape puts on offer, with the source file and the exact query behind every number. This is the first cohort (10 counties, the 10 largest counties by MA enrollment at the 2026-04-01 report month, SSA-keyed); more follow as each cohort clears the quality gate.
Los Angeles County, CA FIPS 06037
975,482 in MA
57.2% penetration
121 plans · 19 parents
Maricopa County, AZ FIPS 04013
420,569 in MA
51.7% penetration
88 plans · 16 parents
Harris County, TX FIPS 48201
405,227 in MA
61.6% penetration
114 plans · 15 parents
Cook County, IL FIPS 17031
399,054 in MA
44.9% penetration
78 plans · 12 parents
Miami-Dade County, FL FIPS 12086
394,102 in MA
75.4% penetration
115 plans · 16 parents
Orange County, CA FIPS 06059
337,204 in MA
56.0% penetration
104 plans · 17 parents
San Diego County, CA FIPS 06073
334,225 in MA
53.8% penetration
93 plans · 16 parents
Riverside County, CA FIPS 06065
285,880 in MA
63.5% penetration
91 plans · 17 parents
Queens County, NY FIPS 36081
257,192 in MA
61.0% penetration
77 plans · 16 parents
Broward County, FL FIPS 12011
245,223 in MA
64.9% penetration
119 plans · 16 parents
Sources: CMS Monthly Enrollment (CPSC) and MA State/County Penetration for 2026-04-01; CMS MA/Part D Landscape 2026. Suppressed cells are ranges, never zeros. Generated 2026-09-15 · the tools behind these pages.