US counties starting with O
78 counties and county-equivalents, which is 2% of the 3,144 in the United States. They are spread across 34 states. Sort any column, or select a county for its map and full data.
Every county beginning with O
| Name | State | Population | Land area | Density | Median income | Seat | FIPS |
|---|---|---|---|---|---|---|---|
| O'Brien County | Iowa | 14,220 | 573 sq mi | 24.8 per sq mi | $68,356 | Primghar | 19141 |
| Oakland County | Michigan | 1,288,337 | 867.4 sq mi | 1,485 per sq mi | $97,760 | Pontiac | 26125 |
| Obion County | Tennessee | 30,067 | 544.9 sq mi | 55.2 per sq mi | $54,613 | Union City | 47131 |
| Ocean County | New Jersey | 673,746 | 628.3 sq mi | 1,072 per sq mi | $89,863 | Toms River | 34029 |
| Oceana County | Michigan | 27,177 | 538.1 sq mi | 50.5 per sq mi | $62,417 | Hart | 26127 |
| Ochiltree County | Texas | 9,284 | 917.7 sq mi | 10.1 per sq mi | $70,183 | Perryton | 48357 |
| Oconee County | Georgia | 44,893 | 184.4 sq mi | 244 per sq mi | $121,217 | Watkinsville | 13219 |
| Oconee County | South Carolina | 83,775 | 626.6 sq mi | 134 per sq mi | $62,388 | Walhalla | 45073 |
| Oconto County | Wisconsin | 40,195 | 997.5 sq mi | 40.3 per sq mi | $75,049 | Oconto | 55083 |
| Ogemaw County | Michigan | 21,121 | 563.5 sq mi | 37.5 per sq mi | $54,666 | West Branch | 26129 |
| Oglala Lakota County | South Dakota | 13,338 | 2,094 sq mi | 6.4 per sq mi | $41,417 | Hot Springs | 46102 |
| Ogle County | Illinois | 51,399 | 758.7 sq mi | 67.8 per sq mi | $82,132 | Oregon | 17141 |
| Oglethorpe County | Georgia | 16,415 | 439.1 sq mi | 37.4 per sq mi | $75,034 | Lexington | 13221 |
| Ohio County | Indiana | 5,994 | 86.2 sq mi | 69.6 per sq mi | $70,392 | Rising Sun | 18115 |
| Ohio County | Kentucky | 23,934 | 587.1 sq mi | 40.8 per sq mi | $57,798 | Hartford | 21183 |
| Ohio County | West Virginia | 40,496 | 106 sq mi | 382 per sq mi | $57,094 | Wheeling | 54069 |
| Okaloosa County | Florida | 221,810 | 929.8 sq mi | 239 per sq mi | $81,998 | Crestview | 12091 |
| Okanogan County | Washington | 45,230 | 5,266 sq mi | 8.6 per sq mi | $63,207 | Okanogan | 53047 |
| Okeechobee County | Florida | 42,608 | 769.3 sq mi | 55.4 per sq mi | $57,984 | Okeechobee | 12093 |
| Okfuskee County | Oklahoma | 11,451 | 618.5 sq mi | 18.5 per sq mi | $48,363 | Okemah | 40107 |
| Oklahoma County | Oklahoma | 822,125 | 708.9 sq mi | 1,160 per sq mi | $66,679 | Oklahoma City | 40109 |
| Okmulgee County | Oklahoma | 37,241 | 697.4 sq mi | 53.4 per sq mi | $54,029 | Okmulgee | 40111 |
| Oktibbeha County | Mississippi | 51,896 | 457.6 sq mi | 113 per sq mi | $46,695 | Starkville | 28105 |
| Oldham County | Kentucky | 70,986 | 187.3 sq mi | 379 per sq mi | $122,497 | La Grange | 21185 |
| Oldham County | Texas | 1,783 | 1,501 sq mi | 1.2 per sq mi | $79,900 | Vega | 48359 |
| Oliver County | North Dakota | 1,898 | 722.4 sq mi | 2.6 per sq mi | $77,240 | Center | 38065 |
| Olmsted County | Minnesota | 166,731 | 653.5 sq mi | 255 per sq mi | $95,406 | Rochester | 27109 |
| Oneida County | Idaho | 5,085 | 1,199 sq mi | 4.2 per sq mi | $74,954 | Malad City | 16071 |
| Oneida County | New York | 226,392 | 1,212 sq mi | 187 per sq mi | $70,154 | Utica | 36065 |
| Oneida County | Wisconsin | 38,131 | 1,114 sq mi | 34.2 per sq mi | $69,371 | Rhinelander | 55085 |
| Onondaga County | New York | 466,584 | 778.4 sq mi | 599 per sq mi | $76,945 | Syracuse | 36067 |
| Onslow County | North Carolina | 217,175 | 762.1 sq mi | 285 per sq mi | $68,148 | Jacksonville | 37133 |
| Ontario County | New York | 113,130 | 644 sq mi | 176 per sq mi | $82,324 | Canandaigua | 36069 |
| Ontonagon County | Michigan | 5,823 | 1,311 sq mi | 4.4 per sq mi | $54,398 | Ontonagon | 26131 |
| Orange County | California | 3,149,507 | 793.2 sq mi | 3,970 per sq mi | $116,289 | Santa Ana | 06059 |
| Orange County | Florida | 1,528,002 | 903.1 sq mi | 1,692 per sq mi | $79,719 | Orlando | 12095 |
| Orange County | Indiana | 19,834 | 398.4 sq mi | 49.8 per sq mi | $65,873 | Paoli | 18117 |
| Orange County | New York | 417,669 | 812.1 sq mi | 514 per sq mi | $97,178 | Goshen | 36071 |
| Orange County | North Carolina | 152,498 | 397.6 sq mi | 384 per sq mi | $90,089 | Hillsborough | 37135 |
| Orange County | Texas | 86,266 | 333.8 sq mi | 258 per sq mi | $72,104 | Orange | 48361 |
| Orange County | Vermont | 30,002 | 687 sq mi | 43.7 per sq mi | $82,232 | Chelsea | 50017 |
| Orange County | Virginia | 40,083 | 340.5 sq mi | 118 per sq mi | $94,008 | Orange | 51137 |
| Orangeburg County | South Carolina | 83,177 | 1,106 sq mi | 75.2 per sq mi | $45,675 | Orangeburg | 45075 |
| Oregon County | Missouri | 8,709 | 789.8 sq mi | 11.0 per sq mi | $43,069 | Alton | 29149 |
| Orleans Parish | Louisiana | 362,154 | 169.6 sq mi | 2,136 per sq mi | $56,631 | New Orleans | 22071 |
| Orleans County | New York | 39,825 | 391.3 sq mi | 102 per sq mi | $65,969 | Albion | 36073 |
| Orleans County | Vermont | 27,600 | 694.6 sq mi | 39.7 per sq mi | $70,103 | Newport | 50019 |
| Osage County | Kansas | 15,693 | 705.5 sq mi | 22.2 per sq mi | $74,467 | Lyndon | 20139 |
| Osage County | Missouri | 13,611 | 606.6 sq mi | 22.4 per sq mi | $76,681 | Linn | 29151 |
| Osage County | Oklahoma | 46,794 | 2,247 sq mi | 20.8 per sq mi | $62,847 | Pawhuska | 40113 |
| Osborne County | Kansas | 3,285 | 892.5 sq mi | 3.7 per sq mi | $63,011 | Osborne | 20141 |
| Osceola County | Florida | 481,718 | 1,327 sq mi | 363 per sq mi | $72,637 | Kissimmee | 12097 |
| Osceola County | Iowa | 5,980 | 398.7 sq mi | 15.0 per sq mi | $69,239 | Sibley | 19143 |
| Osceola County | Michigan | 23,516 | 566.3 sq mi | 41.5 per sq mi | $58,267 | Reed City | 26133 |
| Oscoda County | Michigan | 8,723 | 565.7 sq mi | 15.4 per sq mi | $49,515 | Mio | 26135 |
| Oswego County | New York | 118,569 | 951.6 sq mi | 125 per sq mi | $69,183 | Oswego | 36075 |
| Otero County | Colorado | 17,683 | 1,262 sq mi | 14.0 per sq mi | $54,037 | La Junta | 08089 |
| Otero County | New Mexico | 70,368 | 6,613 sq mi | 10.6 per sq mi | $55,876 | Alamogordo | 35035 |
| Otoe County | Nebraska | 16,531 | 615.6 sq mi | 26.9 per sq mi | $82,188 | Nebraska City | 31131 |
| Otsego County | Michigan | 26,080 | 515 sq mi | 50.6 per sq mi | $68,183 | Gaylord | 26137 |
| Otsego County | New York | 60,589 | 1,002 sq mi | 60.5 per sq mi | $68,885 | Cooperstown | 36077 |
| Ottawa County | Kansas | 5,744 | 720.7 sq mi | 8.0 per sq mi | $74,018 | Minneapolis | 20143 |
| Ottawa County | Michigan | 308,459 | 563.5 sq mi | 547 per sq mi | $90,502 | Grand Haven | 26139 |
| Ottawa County | Ohio | 39,481 | 254.7 sq mi | 155 per sq mi | $76,101 | Port Clinton | 39123 |
| Ottawa County | Oklahoma | 30,438 | 470.8 sq mi | 64.6 per sq mi | $49,947 | Miami | 40115 |
| Otter Tail County | Minnesota | 61,041 | 1,972 sq mi | 31.0 per sq mi | $72,255 | Fergus Falls | 27111 |
| Ouachita County | Arkansas | 21,731 | 732.7 sq mi | 29.7 per sq mi | $49,268 | Camden | 05103 |
| Ouachita Parish | Louisiana | 158,542 | 610.1 sq mi | 260 per sq mi | $54,688 | Monroe | 22073 |
| Ouray County | Colorado | 5,265 | 540.7 sq mi | 9.7 per sq mi | $91,020 | Ouray | 08091 |
| Outagamie County | Wisconsin | 195,894 | 637.6 sq mi | 307 per sq mi | $85,069 | Appleton | 55087 |
| Overton County | Tennessee | 23,787 | 433.5 sq mi | 54.9 per sq mi | $48,959 | Livingston | 47133 |
| Owen County | Indiana | 21,886 | 385.3 sq mi | 56.8 per sq mi | $62,464 | Spencer | 18119 |
| Owen County | Kentucky | 11,601 | 350.5 sq mi | 33.1 per sq mi | $61,134 | Owenton | 21187 |
| Owsley County | Kentucky | 3,932 | 197.4 sq mi | 19.9 per sq mi | $22,188 | Booneville | 21189 |
| Owyhee County | Idaho | 12,661 | 7,668 sq mi | 1.7 per sq mi | $64,406 | Murphy | 16073 |
| Oxford County | Maine | 60,346 | 2,077 sq mi | 29.1 per sq mi | $60,173 | Paris | 23017 |
| Ozark County | Missouri | 9,172 | 745 sq mi | 12.3 per sq mi | $44,163 | Gainesville | 29153 |
| Ozaukee County | Wisconsin | 94,346 | 233 sq mi | 405 per sq mi | $96,996 | Port Washington | 55089 |
Sources: US Census Bureau, Population Estimates Program, Vintage 2025 Population Estimates, released 26 March 2026; US Census Bureau, Gazetteer Files, 2025 Gazetteer Files, released 10 September 2025; US Census Bureau, American Community Survey, American Community Survey 2020-2024 5-Year Estimates, released 29 January 2026. Retrieved 30 August 2026.