Medicare Advantage is a national market only in aggregate. Drawn county by county it is a patchwork of small monopolies: one organisation holds more than half the members in 1,369 of 3,131 counties and more than seven in ten in 459. Against February 2026, the April 2026 file adds 186,557 members nationally and takes them away in 569 counties.
The county map
One measure at a time, on one hue, so the map is read for magnitude rather than decoded from a key. Hover for the county, select it for the organisations holding it, choose a state to zoom. Every figure is Medicare Advantage.
The ten counties reading highest on whatever the map is showing, and the text version of it for anyone who cannot use the map. Counties under 1,000 members are left out: on any share measure they are all ties at the top and none of them is news. Selecting one opens the county below.
Whose ground it is
One map per carrier, shaded where that organisation holds the largest share of the county — the count under each name is how many counties it leads. Twelve fills on a single map cannot be told apart — the palette fails colour-blind separation well before twelve — so identity goes here, one hue at a time. Select one to put its share on the map above. The last tile is every county led by an organisation off the board: the regional Blues, the provider-sponsored plans and the big city locals.
What this page is
Every county fill is a sum of what CMS disclosed for one organisation in one county in the April 2026 contract/plan/state/county file, compared with February 2026. Nothing is modelled, smoothed or interpolated. Figures are Medicare Advantage only — local and regional coordinated care plans, PFFS and MSA; Standalone Part D, employer-only direct-contract PDP, cost plans and PACE are excluded and do not read across to Medicaid, Commercial or Exchange.
The default measure is a rate rather than a count. A choropleth of members rewards land area — Los Angeles and Loving County get one polygon each — so concentration, share and change lead, and the members view is there for orientation and should be read against the list under it.
Cells CMS masks — an organisation with ten or fewer members in a county — are excluded from every county total and every share. That is about 1.1% of members nationally and more in small counties, so a county reading as unheld may hold a few hundred members across several small organisations. 10 areas holding 14,442 members cannot be drawn — the enrolment file is keyed on SSA area codes and the boundary file on FIPS, and these have no county to put a shape on: ssa:07140 (4,032); St. John, VI (3,028); ssa:07120 (2,776); St. Croix, VI (2,489); Falls Church City, VA (626).
Provenance
- Members — CMS Monthly Enrollment by CPSC, April 2026 against February 2026. The dashboard on The Count reads the plan file for May 2026; where the two months differ, the county file is the later one CMS has published.
- Boundaries — US Census cartographic boundary files via us-atlas, Albers USA. Puerto Rico is absent from that projection and is drawn as a separate inset.
- Area keys — aggregation is on the SSA area code, not FIPS. Several SSA areas share one FIPS county and roughly ten thousand rows a month carry no FIPS at all; summing on FIPS merges them and drops about 240,000 members out of Los Angeles alone.
- Licence — US Government public domain, US Census boundaries public domain.
How this page maintains itself
- Built by the same monthly job that builds The Count, from the same two files, with no network call at view time — the geometry is in the page.
- Movement figures pass the reassignment gate before they are drawn. A county where a book changed hands is drawn as having no reading rather than as a carrier winning ground.
- The publish gate checks the drawn coverage, the payload's internal arithmetic and every figure in the opening paragraph before this page is allowed into the site.