Which counties should you actually work?
Across 3,199 counties, Medicare Advantage now covers 51.6% of Medicare beneficiaries — but the county spread runs from under 5% to over 90%. 1,462 counties are already majority-MA, and 2,359 of 3,197 gained share in the last twelve months. Filter the whole country below, then drill into any market.
MA penetration is the share of a county's Medicare beneficiaries enrolled in a Medicare Advantage or other managed-care plan, rather than Original Medicare. A county at 70% means seven in ten local beneficiaries already carry an MA card.
Penetration change is that share today minus the same month a year ago, in percentage points. It is the cleanest read on momentum, because it strips out the fact that the Medicare population itself is growing everywhere.
Two counties can look identical on penetration and behave completely differently: a mature 70% county that gained 0.2 points is saturated, while a 40% county that gained 3 points is in play. That is why the charts below plot both at once.
Penetration across the country, in three dimensions
Filter the country
Penetration × momentum × market size
Each ball is one county. Push it right and MA already owns the market. Push it up and MA is still taking share. Push it back and the county is big.
The interesting corner is left, high and far back: a large county where penetration is still low but climbing. That is a market with room and proof that people will switch. The right and flat corner is the opposite — big MA book, no headroom, and a retention problem rather than a growth one.
Every county, ranked
| County | Medicare benes | MA enrollees | Penetration | Share gained (12 mo) |
|---|---|---|---|---|
| Los Angeles County, CA | 1,707,013 | 977,518 | 57.3% | +0.8 pp |
| Maricopa County, AZ | 812,942 | 416,326 | 51.2% | +0.3 pp |
| Harris County, TX | 660,955 | 403,606 | 61.1% | +0.8 pp |
| Cook County, IL | 886,637 | 397,598 | 44.8% | +0.3 pp |
| Miami-Dade County, FL | 522,929 | 394,113 | 75.4% | +0.1 pp |
| Orange County, CA | 603,122 | 336,367 | 55.8% | +0.4 pp |
| San Diego County, CA | 622,423 | 333,391 | 53.6% | +0.3 pp |
| Riverside County, CA | 452,145 | 285,671 | 63.2% | +0.1 pp |
| Queens County, NY | 421,274 | 256,687 | 60.9% | +0.9 pp |
| Broward County, FL | 378,471 | 245,532 | 64.9% | +0.1 pp |
| Clark County, NV | 425,652 | 241,613 | 56.8% | +0.8 pp |
| Kings County, NY | 412,291 | 237,215 | 57.5% | +0.8 pp |
| San Bernardino County, CA | 349,071 | 234,984 | 67.3% | +0.6 pp |
| Wayne County, MI | 352,170 | 228,690 | 64.9% | +0.6 pp |
| Dallas County, TX | 365,246 | 200,443 | 54.9% | +0.9 pp |
| Bexar County, TX | 340,477 | 199,897 | 58.7% | +0.9 pp |
| King County, WA | 366,334 | 197,185 | 53.8% | +0.1 pp |
| Allegheny County, PA | 283,061 | 194,676 | 68.8% | +0.5 pp |
| Sacramento County, CA | 294,658 | 183,017 | 62.1% | +1.5 pp |
| Tarrant County, TX | 324,205 | 181,174 | 55.9% | +0.5 pp |
| Palm Beach County, FL | 369,794 | 177,895 | 48.1% | +0.2 pp |
| Hillsborough County, FL | 274,542 | 171,125 | 62.3% | +0.7 pp |
| Bronx County, NY | 232,893 | 165,890 | 71.2% | +0.9 pp |
| Cuyahoga County, OH | 280,504 | 161,661 | 57.6% | -0.9 pp |
| Philadelphia County, PA | 266,209 | 160,736 | 60.4% | +0.6 pp |
| Pinellas County, FL | 263,518 | 159,550 | 60.5% | +0.3 pp |
| Santa Clara County, CA | 312,175 | 157,148 | 50.3% | +0.5 pp |
| Erie County, NY | 217,374 | 155,472 | 71.5% | +0.7 pp |
| Oakland County, MI | 278,023 | 154,644 | 55.6% | +0.7 pp |
| Pima County, AZ | 262,707 | 151,172 | 57.5% | +0.8 pp |
| Alameda County, CA | 277,446 | 145,720 | 52.5% | +0.9 pp |
| New York County, NY | 299,215 | 141,508 | 47.3% | +0.1 pp |
| Orange County, FL | 226,923 | 139,741 | 61.6% | +0.8 pp |
| Monroe County, NY | 175,280 | 134,615 | 76.8% | +0.1 pp |
| Capitol Planning Region, CT | 210,576 | 133,932 | 63.6% | -0.1 pp |
| St. Louis County, MO | 227,629 | 130,775 | 57.5% | +0.7 pp |
| Hennepin County, MN | 229,123 | 130,693 | 57.0% | -4.4 pp |
| Polk County, FL | 182,917 | 125,371 | 68.5% | +1.2 pp |
| Macomb County, MI | 198,361 | 119,748 | 60.4% | +1.0 pp |
| Contra Costa County, CA | 228,184 | 118,563 | 52.0% | -0.7 pp |
| Franklin County, OH | 210,247 | 117,678 | 56.0% | -1.3 pp |
| El Paso County, TX | 153,595 | 114,282 | 74.4% | +1.3 pp |
| Honolulu County, HI | 208,156 | 113,514 | 54.5% | -0.2 pp |
| Lee County, FL | 225,678 | 113,210 | 50.2% | +0.6 pp |
| Milwaukee County, WI | 165,643 | 112,172 | 67.7% | +0.7 pp |
| Volusia County, FL | 172,984 | 105,199 | 60.8% | +0.6 pp |
| Middlesex County, MA | 307,378 | 105,177 | 34.2% | -0.2 pp |
| Duval County, FL | 195,123 | 104,034 | 53.3% | +0.6 pp |
| Pasco County, FL | 152,703 | 102,843 | 67.3% | +0.7 pp |
| Nassau County, NY | 303,097 | 101,181 | 33.4% | +0.7 pp |
| Suffolk County, NY | 334,556 | 100,621 | 30.1% | +0.7 pp |
| Wake County, NC | 190,745 | 100,238 | 52.6% | +0.6 pp |
| Hidalgo County, TX | 125,198 | 96,699 | 77.2% | +1.4 pp |
| Salt Lake County, UT | 166,087 | 96,553 | 58.1% | +1.2 pp |
| Brevard County, FL | 182,756 | 93,172 | 51.0% | +0.6 pp |
| Jefferson County, AL | 138,955 | 93,070 | 67.0% | +0.7 pp |
| Hamilton County, OH | 164,245 | 92,856 | 56.5% | -0.9 pp |
| Mecklenburg County, NC | 167,689 | 92,774 | 55.3% | +0.6 pp |
| Kent County, MI | 125,764 | 92,411 | 73.5% | +0.9 pp |
| Marion County, IN | 159,399 | 92,048 | 57.7% | +0.4 pp |
| Pierce County, WA | 175,141 | 91,162 | 52.1% | +0.9 pp |
| Snohomish County, WA | 151,910 | 90,969 | 59.9% | +0.4 pp |
| Multnomah County, OR | 138,113 | 90,786 | 65.7% | -0.5 pp |
| Fulton County, GA | 163,659 | 88,631 | 54.2% | +0.5 pp |
| Providence County, RI | 132,907 | 86,127 | 64.8% | +0.8 pp |
| Bernalillo County, NM | 142,494 | 84,210 | 59.1% | +0.5 pp |
| Marion County, FL | 135,204 | 82,339 | 60.9% | +1.2 pp |
| Jefferson County, KY | 162,105 | 81,795 | 50.5% | +0.6 pp |
| San Francisco County, CA | 159,389 | 81,776 | 51.3% | +1.3 pp |
| Worcester County, MA | 182,190 | 80,935 | 44.4% | +0.2 pp |
| Shelby County, TN | 167,409 | 80,425 | 48.0% | +1.0 pp |
| Summit County, OH | 126,267 | 80,321 | 63.6% | -0.7 pp |
| Guilford County, NC | 111,884 | 79,246 | 70.8% | +1.0 pp |
| Fresno County, CA | 161,203 | 78,165 | 48.5% | +0.4 pp |
| Westchester County, NY | 198,268 | 77,447 | 39.1% | +0.7 pp |
| Jackson County, MO | 136,399 | 77,047 | 56.5% | +0.5 pp |
| Jefferson County, CO | 124,114 | 76,981 | 62.0% | -0.3 pp |
| Gwinnett County, GA | 131,743 | 76,906 | 58.4% | +1.1 pp |
| Travis County, TX | 160,221 | 76,480 | 47.7% | 0.0 pp |
| Fort Bend County, TX | 135,739 | 75,678 | 55.8% | +1.0 pp |
| South Central Connecticut Planning Region, CT | 123,841 | 74,593 | 60.2% | 0.0 pp |
| Westmoreland County, PA | 102,412 | 73,532 | 71.8% | +0.6 pp |
| Montgomery County, OH | 119,866 | 73,367 | 61.2% | -0.2 pp |
| Lake County, FL | 127,351 | 73,002 | 57.3% | +1.0 pp |
| Ventura County, CA | 177,135 | 72,985 | 41.2% | -0.6 pp |
| San Mateo County, CA | 143,201 | 72,864 | 50.9% | +0.6 pp |
| Clark County, WA | 107,639 | 72,541 | 67.4% | +0.5 pp |
| Dekalb County, GA | 120,072 | 71,567 | 59.6% | +0.6 pp |
| Montgomery County, PA | 192,090 | 71,251 | 37.1% | 0.0 pp |
| Sarasota County, FL | 166,313 | 71,175 | 42.8% | -0.1 pp |
| Bergen County, NJ | 194,051 | 71,057 | 36.6% | +0.6 pp |
| Dupage County, IL | 186,207 | 70,626 | 37.9% | 0.0 pp |
| San Joaquin County, CA | 128,714 | 70,478 | 54.8% | +1.0 pp |
| Spokane County, WA | 122,464 | 70,288 | 57.4% | +0.8 pp |
| Collin County, TX | 160,032 | 69,027 | 43.1% | +0.2 pp |
| Washington County, OR | 106,147 | 67,908 | 64.0% | -0.5 pp |
| Jefferson Parish, LA | 94,448 | 67,522 | 71.5% | +0.5 pp |
| Genesee County, MI | 97,327 | 67,170 | 69.0% | +1.3 pp |
| Tulsa County, OK | 128,840 | 67,166 | 52.1% | +1.1 pp |
| Oklahoma County, OK | 146,912 | 66,930 | 45.6% | +0.8 pp |
Without JavaScript this table shows the 100 largest MA markets. With JavaScript it shows every county matching your filters.
Where this comes from
Every figure on this page is computed at build time from the
CMS
Medicare Monthly Enrollment file, county geography level
(BENE_GEO_LVL=County), April 2026, compared against
April 2025 from the same file.
Penetration here uses the monthly-file basis: MA_AND_OTH_BENES ÷ TOT_BENES. That
numerator includes cost plans, PACE and other managed-care arrangements alongside Medicare
Advantage, so it sits above the pure-MA plan-year figure quoted elsewhere on the site. Both bases
are documented at Methodology → penetration bases.
CMS suppresses cells with fewer than 11 beneficiaries; those counties are shown with an em dash rather than a zero. County rows labelled “Unknown” and out-of-country beneficiaries are excluded, which is why the county totals here fall a little short of the published national count.
Counties covered: 3,199 · with a year-ago comparison: 3,197 · plotted on the map: 3,107 (Puerto Rico and the Virgin Islands appear in the table and CSV but not on the continental map projection).