There are 23 counties in the U.S. state of Wyoming. There were originally five counties in the Wyoming Territory: Laramie and Carter, established in 1867; Carbon and Albany established in 1868; and Uinta, and annexed portion of Utah and Idaho, extending from Montana (including Yellowstone Park) to the Wyoming–Utah boundary. On July 10, 1890, Wyoming was admitted to the Union with thirteen counties in it. Ten more counties were created after statehood.

Two counties were renamed after their creation. Carter County was renamed Sweetwater County on December 1, 1869. Pease County, formed in 1875, was renamed Johnson County in 1879.

The Federal Information Processing Standard (FIPS) code, which is used by the United States government to uniquely identify states and counties, is provided with each entry. Wyoming's code is 56, which when combined with any county code would be written as 56XXX. The FIPS code for each county links to census data for that county.

County	FIPS code	County seat	Est.	Formed from	Etymology	Population	Area	Map
Albany County	001	Laramie	1868	One of the original five counties.	City of Albany, New York, from which early settlers hailed.	38,257	4,274 sq mi (11,070 km)
Big Horn County	003	Basin	1896	Parts of Sheridan County, Johnson County, and Fremont County.	Big Horn Mountains, a mountain range extending into northern Wyoming	12,018	3,137 sq mi (8,125 km)
Campbell County	005	Gillette	1911	Parts of Weston County and Crook County.	John Allen Campbell (1835–80), first governor of the Wyoming Territory (1869–75)	47,498	4,797 sq mi (12,424 km)
Carbon County	007	Rawlins	1868	One of the original five counties.	The vast coal beds in the county.	14,334	7,897 sq mi (20,453 km)
Converse County	009	Douglas	1888	Parts of Albany County and Laramie County.	Amasa Rice Converse (1842–1885), a banker and rancher from Cheyenne, Wyoming.	13,809	4,255 sq mi (11,020 km)
Crook County	011	Sundance	1875	Parts of Laramie County and Albany County.	General George Crook (1828–90), who served in the American Civil War and the Indian Wars.	7,592	2,859 sq mi (7,405 km)
Fremont County	013	Lander	1884	Part of Sweetwater County.	John C. Frémont (1813–90), explorer, U.S. Senator for California, and the first presidential candidate of a major party to run on a platform in opposition to slavery	39,815	9,183 sq mi (23,784 km)
Goshen County	015	Torrington	1911	Part of Laramie County.	The Land of Goshen, a Biblical paradise.	12,642	2,225 sq mi (5,763 km)
Hot Springs County	017	Thermopolis	1911	Parts of Fremont County, Big Horn County, and Park County.	The hot springs at Thermopolis within the county borders.	4,661	2,004 sq mi (5,190 km)
Johnson County	019	Buffalo	1875	Parts of Carbon County and Sweetwater County.	Edward P. Johnson (1843–1879), a lawyer from Cheyenne, Wyoming. (Initial name, Pease County, named for E. L. Pease, President of the Territorial Legislative Council.)	8,759	4,166 sq mi (10,790 km)
Laramie County	021	Cheyenne	1867	One of the original five counties.	Jacques La Ramee (1785?–1821), a French-Canadian fur trapper.	100,984	2,686 sq mi (6,957 km)
Lincoln County	023	Kemmerer	1911	Part of Uinta County.	Abraham Lincoln (1809–65), U.S. President (1861–65)	20,880	4,069 sq mi (10,539 km)
Natrona County	025	Casper	1888	Part of Carbon County.	The natron, or soda deposits found within the county's borders. Natrona means natron in Spanish.	79,941	5,340 sq mi (13,831 km)
Niobrara County	027	Lusk	1911	Part of Converse County.	The Niobrara River, which flows through the state. Niobrara is Omaha for flat or broad river.	2,354	2,626 sq mi (6,801 km)
Park County	029	Cody	1909	Part of Big Horn County.	Yellowstone National Park	30,735	6,943 sq mi (17,982 km)
Platte County	031	Wheatland	1911	Part of Laramie County.	North Platte River. Plate is French for flat.	8,546	2,085 sq mi (5,400 km)
Sheridan County	033	Sheridan	1888	Part of Johnson County.	Philip Sheridan (1831–88), American Civil War general.	32,519	2,523 sq mi (6,535 km)
Sublette County	035	Pinedale	1921	Parts of Fremont County and Lincoln County.	William Sublette, pioneer and fur trapper.	8,969	4,882 sq mi (12,644 km)
Sweetwater County	037	Green River	1867	One of the original five counties.	Sweetwater River (a tributary of the North Platte River), which flows through the state. (Original name, Carter County, named for sutler William Alexander Carter.)	41,249	10,426 sq mi (27,003 km)
Teton County	039	Jackson	1921	Part of Lincoln County.	Teton Range, a small mountain range of the Rocky Mountains at the Wyoming–Idaho state line	23,232	4,008 sq mi (10,381 km)
Uinta County	041	Evanston	1869	One of the original five counties.	The Uinta Mountains, named in turn after the Uintah Native American people.	20,745	2,082 sq mi (5,392 km)
Washakie County	043	Worland	1911	Part of Big Horn County	Washakie (1804–1900), a leader of Shoshone Native American tribe.	7,710	2,240 sq mi (5,802 km)
Weston County	045	Newcastle	1890	Part of Crook County	John Weston (1831–95), who was responsible for bringing the first railroad to the area.	6,808	2,398 sq mi (6,211 km)