Growth in Medicare Advantage by organizational size across rural and urban counties

To understand the changing landscape of Medicare Advantage (MA) markets in urban and rural counties with particular focus on the size of MA organizations. With MA covering more than half of all Medicare enrollees and notably different health and access conditions in rural areas, understanding the extent of participation in MA markets in both urban and rural areas is critical. In this paper, we establish which organizations are offering MA plans and which organizations' plans are being chosen by eligible Medicare beneficiaries.

Data on MA plan availability, parent organizations, and enrollment for 2019 through 2026 were obtained from CMS websites. Classification of counties was based on 2024 Urban Influence Codes (UIC): metropolitan (1, 4); micropolitan (2, 5, 7); nonmetropolitan (3, 6, 8, 9). We offer a taxonomy of MA organizations based on the number of states where MA organizations offer plans: national (29-50 states), large regional (6-18 states), small regional (2-5 states), local (1 state).

The overall size of the MA population grew 59% from 2019 to 2025, including doubling growth in the most rural counties. The proportion of the MA population enrolled in plans from national MA organizations and small regional organizations has increased monotonically over this period. Notably, this trend has featured across both urban and rural counties. Enrollment in plans from local MA organizations has declined across all geographic locations.

National MA organizations continue to dominate the landscape across both urban and rural counties, with nearly 65% of total enrollment in 2025. Moreover, over 80% of the growth in available plans from 2019 to 2025 were offered by these same four or five organizations.