| County | Rank | Change (2020) ↓ | 2025 Pop. | 2020 Pop. |
|---|---|---|---|---|
| Union County | 1 | 19.14% | 75,159 | 63,085 |
| Delaware County | 2 | 12.4% | 241,856 | 215,166 |
| Pickaway County | 3 | 7.82% | 63,244 | 58,656 |
| Fairfield County | 4 | 6.72% | 170,168 | 159,448 |
| Madison County | 5 | 6.37% | 46,644 | 43,849 |
| Athens County | 6 | 6.35% | 66,356 | 62,393 |
| Warren County | 7 | 5.65% | 256,974 | 243,228 |
| Licking County | 8 | 4.08% | 186,073 | 178,784 |
| Morrow County | 9 | 3.24% | 36,113 | 34,980 |
| Miami County | 10 | 2.98% | 112,202 | 108,959 |
| Clermont County | 11 | 2.78% | 214,558 | 208,750 |
| Lorain County | 12 | 2.61% | 321,668 | 313,498 |
| Butler County | 13 | 2.25% | 399,673 | 390,878 |
| Coshocton County | 14 | 2.17% | 37,377 | 36,584 |
| Wood County | 15 | 1.82% | 134,666 | 132,256 |
| Greene County | 16 | 1.72% | 171,019 | 168,131 |
| Portage County | 17 | 1.64% | 164,511 | 161,853 |
| Highland County | 18 | 1.46% | 43,990 | 43,359 |
| Medina County | 19 | 1.37% | 185,148 | 182,646 |
| Noble County | 20 | 1.37% | 14,283 | 14,090 |
| Knox County | 21 | 1.22% | 63,568 | 62,803 |
| Defiance County | 22 | 1.12% | 38,689 | 38,262 |
| Champaign County | 23 | 0.79% | 39,049 | 38,743 |
| Franklin County | 24 | 0.78% | 1,334,729 | 1,324,441 |
| Carroll County | 25 | 0.75% | 26,902 | 26,702 |
| Perry County | 26 | 0.75% | 35,711 | 35,446 |
| Adams County | 27 | 0.75% | 27,645 | 27,440 |
| Brown County | 28 | 0.59% | 43,931 | 43,673 |
| Holmes County | 29 | 0.41% | 44,408 | 44,227 |
| Muskingum County | 30 | 0.25% | 86,687 | 86,468 |
| Sandusky County | 31 | 0.23% | 58,993 | 58,856 |
| Hamilton County | 32 | 0.16% | 831,732 | 830,377 |
| Ashland County | 33 | 0.1% | 52,522 | 52,470 |
| Clinton County | 34 | 0.01% | 42,034 | 42,028 |
| Marion County | 35 | -0.08% | 65,335 | 65,388 |
| Logan County | 36 | -0.15% | 46,047 | 46,116 |
| Geauga County | 37 | -0.16% | 95,239 | 95,387 |
| Mercer County | 38 | -0.17% | 42,469 | 42,542 |
| Jackson County | 39 | -0.2% | 32,596 | 32,662 |
| Richland County | 40 | -0.24% | 124,670 | 124,966 |
| Pike County | 41 | -0.34% | 26,979 | 27,072 |
| Wayne County | 42 | -0.43% | 116,426 | 116,923 |
| Shelby County | 43 | -0.45% | 47,927 | 48,146 |
| Lake County | 44 | -0.46% | 231,448 | 232,516 |
| Auglaize County | 45 | -0.46% | 46,258 | 46,472 |
| Hancock County | 46 | -0.49% | 74,564 | 74,928 |
| Montgomery County | 47 | -0.5% | 534,440 | 537,119 |
| Stark County | 48 | -0.52% | 372,578 | 374,522 |
| Huron County | 49 | -0.57% | 58,159 | 58,495 |
| Henry County | 50 | -0.58% | 27,508 | 27,668 |
| Fayette County | 51 | -0.65% | 28,787 | 28,975 |
| Guernsey County | 52 | -0.72% | 38,147 | 38,423 |
| Ross County | 53 | -0.73% | 76,487 | 77,049 |
| Summit County | 54 | -0.77% | 535,661 | 539,821 |
| Ashtabula County | 55 | -0.9% | 96,615 | 97,495 |
| Seneca County | 56 | -0.98% | 54,513 | 55,054 |
| Trumbull County | 57 | -1% | 199,667 | 201,681 |
| Crawford County | 58 | -1.06% | 41,569 | 42,013 |
| Clark County | 59 | -1.12% | 134,366 | 135,887 |
| Gallia County | 60 | -1.15% | 28,898 | 29,233 |
| Paulding County | 61 | -1.15% | 18,594 | 18,811 |
| Morgan County | 62 | -1.18% | 13,600 | 13,762 |
| Preble County | 63 | -1.19% | 40,520 | 41,007 |
| Putnam County | 64 | -1.3% | 33,937 | 34,385 |
| Hardin County | 65 | -1.32% | 30,322 | 30,727 |
| Mahoning County | 66 | -1.34% | 224,944 | 228,009 |
| Darke County | 67 | -1.35% | 51,193 | 51,893 |
| Van Wert County | 68 | -1.42% | 28,504 | 28,916 |
| Williams County | 69 | -1.62% | 36,477 | 37,078 |
| Tuscarawas County | 70 | -1.62% | 91,680 | 93,193 |
| Allen County | 71 | -1.77% | 100,320 | 102,125 |
| Lucas County | 72 | -1.82% | 423,014 | 430,859 |
| Ottawa County | 73 | -2.04% | 39,473 | 40,296 |
| Columbiana County | 74 | -2.2% | 99,408 | 101,642 |
| Fulton County | 75 | -2.21% | 41,705 | 42,646 |
| Monroe County | 76 | -2.4% | 13,029 | 13,350 |
| Jefferson County | 77 | -2.53% | 63,532 | 65,178 |
| Wyandot County | 78 | -2.73% | 21,267 | 21,864 |
| Washington County | 79 | -2.77% | 57,995 | 59,647 |
| Cuyahoga County | 80 | -2.95% | 1,225,276 | 1,262,573 |
| Scioto County | 81 | -3.14% | 71,529 | 73,848 |
| Erie County | 82 | -3.18% | 73,077 | 75,481 |
| Meigs County | 83 | -3.52% | 21,379 | 22,159 |
| Hocking County | 84 | -3.77% | 26,984 | 28,040 |
| Belmont County | 85 | -3.81% | 63,764 | 66,292 |
| Vinton County | 86 | -4.16% | 12,268 | 12,801 |
| Harrison County | 87 | -4.94% | 13,775 | 14,491 |
| Lawrence County | 88 | -5.03% | 55,210 | 58,137 |
Ohio's counties show varied growth patterns from 2020 to 2025. Union County leads with 19.14% annualized growth, followed by Delaware County (12.4%) and Pickaway County (7.82%). The largest counties are Franklin County (1,334,729), Cuyahoga County (1,225,276), and Hamilton County (831,732). Of the 88 counties in Ohio, 34 are growing while 54 have experienced population decline. Overall, counties averaged 0.21% annualized growth, with total population growing by 0.34% annually.