The following is a sortable table of the most populous county in each U.S. state, federal district, and territory. Counties and states/territories in bold have a population of at least 1 million.
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| State federal district or territory | Largest county parish or municipality | Population (2013 estimate)[1] | County parish seat or shire town | State federal district or territory population (2013 estimate)[2] | Largest county/parish or municipality Percentage of state/federal district or territory population | |
|---|---|---|---|---|---|---|
| 659,479 | 4,833,722 | 13.64% | ||||
| 300,950 | 735,132 | 40.94% | ||||
| 31,329[3] | — | 55,519 | 56.42% | |||
| Maricopa | 4,009,412 | 6,626,624 | 60.50% | |||
| 391,284 | 2,959,373 | 13.22% | ||||
| Los Angeles | 10,017,068 | 38,332,521 | 26.13% | |||
| 655,044 | 5,268,367 | 12.43% | ||||
| 939,904 | 3,596,080 | 26.14% | ||||
| 549,684 | 925,749 | 59.38% | ||||
| 693,972 | 693,972 | 100% | ||||
| Miami-Dade | 2,617,176 | 19,552,860 | 13.39% | |||
| Fulton | 1,010,562 | 10,214,860 | 9.85% | |||
| 162,742 | 162,742 | 100% | ||||
| 983,429 | 1,404,054 | 70.04% | ||||
| 416,464 | 1,612,136 | 25.83% | ||||
| Cook | 5,240,700 | 12,882,135 | 40.68% | |||
| 928,281 | 6,570,902 | 14.13% | ||||
| 451,677 | 3,090,416 | 14.62% | ||||
| 566,933 | 2,893,957 | 19.59% | ||||
| 756,832 | 4,395,295 | 17.22% | ||||
| 445,227 | 4,625,470 | 9.63% | ||||
| 285,456 | 1,328,302 | 21.49% | ||||
| Montgomery | 1,016,677 | 5,928,814 | 17.15% | |||
| Middlesex | 1,552,802 | 6,692,824 | 23.20% | |||
| Wayne | 1,775,273 | 9,895,622 | 17.94% | |||
| Hennepin | 1,198,778 | 5,420,380 | 22.12% | |||
| 244,899 | 2,991,207 | 8.19% | ||||
| St. Louis | 1,001,444 | 6,044,171 | 16.57% | |||
| 154,162 | 1,015,165 | 15.19% | ||||
| 531,265 | 1,868,516 | 28.43% | ||||
| Clark | 2,027,868 | 2,790,136 | 72.68% | |||
| 402,922 | 1,323,459 | 30.44% | ||||
| 925,328 | 8,899,339 | 10.40% | ||||
| 673,460 | 2,085,287 | 32.30% | ||||
| Kings | 2,592,149 | 19,651,127 | 13.19% | |||
| Wake[4] | 990,977 | Raleigh | 9,848,060 | 10.06% | ||
| 162,829 | 723,393 | 22.51% | ||||
| 48,220 | 52,263 | 92.26% | ||||
| Franklin[5] | 1,268,154 | Columbus | 11,570,808 | 10.96% | ||
| 755,245 | 3,850,568 | 19.61% | ||||
| 759,256 | 3,930,065 | 19.32% | ||||
| Philadelphia | 1,553,165 | 12,773,801 | 12.16% | |||
| 395,326 | 3,337,177 | 11.84% | ||||
| 628,323 | 1,051,511 | 59.75% | ||||
| 474,266 | 4,774,839 | 9.93% | ||||
| 179,640 | 844,877 | 21.26% | ||||
| 940,764 | 6,495,978 | 14.48% | ||||
| Harris | 4,336,853 | 26,448,193 | 16.40% | |||
| (100) | (none) | (160) | 62.5% | |||
| Salt Lake | 1,063,842 | 2,900,872 | 36.67% | |||
| 158,504 | 626,630 | 25.29% | ||||
| 51,634 | — | 104,901 | 49.22% | |||
| Fairfax | 1,116,897 | 8,260,405 | 13.52% | |||
| King | 2,044,449 | 6,971,406 | 29.33% | |||
| 191,275 | 1,854,304 | 10.32% | ||||
| 956,023 | 5,742,713 | 16.65% | ||||
| 95,809 | 582,658 | 16.44% |