Natrona County is a county in the U.S. state of Wyoming. As of the 2020 United States Census, the population was 79,955, making it the second-most populous county in Wyoming. Its county seat is Casper.

Natrona County comprises the Casper, WY Metropolitan Statistical Area. In 2010, the center of population of Wyoming was in Natrona County, near Alcova.

Prior to Wyoming's settlement by European-based populations, the area's stretches played host to nomadic tribes such as Cheyenne, Arapaho, Shoshone, and Sioux.

New York investor John Jacob Astor established the settlement of Astoria on the Columbia River, and sent Robert Stuart eastward to blaze a trail and lay the foundation of a string of trading posts. Stuart documented the South Pass Route through the Continental Divide, near the SW corner of present-day Natrona County. Stuart's company erected the first hut in the area in 1812, near present-day Bessemer Bend.

In 1840, Father Pierre-Jean De Smet began preaching the Christian teaching to this area's indigenous peoples. He carved his name on Independence Rock and called it The Register of the Desert. Later explorers who inscribed the rock include John C. Frémont (1843), who explored the country along the Platte and Sweetwater Rivers.

The first Euro-American settlement occurred in the Casper area in the late 19th century. Natrona County was created by the legislature of the Wyoming Territory on March 9, 1888, and it was organized in 1890. The land for Natrona County was annexed from Carbon County.

Natrona County was named for the deposits of natron found in the area. According to George Mitchell, first mayor of Casper and member of the organization commission for Natrona County, the name was first suggested "by my old friend the late Cy Iba, who at one time owned the soda lakes." In 1909, Natrona County gained land from Fremont County. The boundaries were adjusted slightly in 1911 and 1931, and at that point the county gained its present outline.

According to the U.S. Census Bureau, the county has an area of 5,376 square miles (13,920 km), of which 5,340 square miles (13,800 km) is land and 35 square miles (91 km) (0.7%) is water.

• Interstate 25
• I-25 BL
• U.S. Highway 20
• U.S. Highway 26
• U.S. Highway 87
• U.S. Highway 287
• Wyoming Highway 220
• Wyoming Highway 251
• Wyoming Highway 252
• Wyoming Highway 253
• Wyoming Highway 256
• Wyoming Highway 257
• Wyoming Highway 258
• Wyoming Highway 259
• Wyoming Highway 387
• Wyoming Highway 487

• Casper Area Transit
• Express Arrow

Natrona County derives its name from the vast deposits of the mineral Natron found within the county. Of the 18 million tons of Natron consumed by American industry annually 17 Million tons is mined in Wyoming due to it purity.

• Medicine Bow National Forest (part)
• Pathfinder National Wildlife Refuge (part)

Historical population

Census	Pop.	Note	%±
1890	1,094		—
1900	1,785		63.2%
1910	4,766		167.0%
1920	14,635		207.1%
1930	24,272		65.8%
1940	23,858		−1.7%
1950	31,437		31.8%
1960	49,623		57.8%
1970	51,264		3.3%
1980	71,856		40.2%
1990	61,226		−14.8%
2000	66,533		8.7%
2010	75,450		13.4%
2020	79,955		6.0%
2023 (est.)	79,941		0.0%
US Decennial Census 1870–2000 2010–2020

As of the 2000 United States Census, of 2000, there were 66,533 persons, 26,819 households, and 17,754 families in the county. The population density was 12 people per square mile (4.6 people/km). There were 29,882 housing units at an average density of 6 units per square mile (2.3 units/km). The racial makeup of the county was 94.15% White, 0.76% Black or African American, 1.03% Native American, 0.42% Asian, 0.04% Pacific Islander, 1.92% from other races, and 1.68% from two or more races. 4.90% of the population were Hispanic or Latino of any race. 24.6% were of German, 11.6% English, 11.3% American and 11.2% Irish ancestry.

There were 26,819 households, out of which 32.20% had children under the age of 18 living with them, 51.40% were married couples living together, 10.60% had a female householder with no husband present, and 33.80% were non-families. 27.50% of all households were made up of individuals, and 9.40% had someone living alone who was 65 years of age or older. The average household size was 2.42 and the average family size was 2.95.

The county population contained 26.00% under the age of 18, 10.10% from 18 to 24, 27.90% from 25 to 44, 23.30% from 45 to 64, and 12.70% who were 65 years of age or older. The median age was 36 years. For every 100 females there were 97.70 males. For every 100 females age 18 and over, there were 95.00 males.

The median income for a household in the county was $36,619, and the median income for a family was $45,575. Males had a median income of $33,524 versus $21,374 for females. The per capita income for the county was $18,913. About 8.70% of families and 11.80% of the population were below the poverty line, including 16.20% of those under age 18 and 7.20% of those age 65 or over.

As of the 2010 United States Census, there were 75,450 people, 30,616 households, and 19,714 families in the county. The population density was 14.1 people per square mile (5.4 people/km). There were 33,807 housing units at an average density of 6.3 units per square mile (2.4 units/km). The racial makeup of the county was 92.8% white, 1.0% American Indian, 0.9% black or African American, 0.7% Asian, 0.1% Pacific islander, 2.2% from other races, and 2.4% from two or more races. Those of Hispanic or Latino origin made up 6.9% of the population. In terms of ancestry, 27.2% were German, 15.2% were Irish, 13.2% were English, and 10.7% were American.

Of the 30,616 households, 31.9% had children under the age of 18 living with them, 48.1% were married couples living together, 10.9% had a female householder with no husband present, 35.6% were non-families, and 28.5% of all households were made up of individuals. The average household size was 2.41 and the average family size was 2.94. The median age was 36.8 years.

The median income for a household in the county was $50,936 and the median income for a family was $62,859. Males had a median income of $47,610 versus $30,664 for females. The per capita income for the county was $28,235. About 5.4% of families and 8.4% of the population were below the poverty line, including 9.9% of those under age 18 and 8.8% of those age 65 or over.

• Casper (county seat and largest municipality)

Like almost all of Wyoming, Natrona is a heavily Republican county. It is rather conservative for an urban county, having gone Republican in all but three elections since 1944. No Democratic presidential candidate has won forty percent of the county's vote since Lyndon Johnson garnered 52 percent in his 1964 landslide against Barry Goldwater. Bill Clinton did win a 100-vote plurality in the 1992 election due to a significant third-party vote. In 2024, Donald Trump received 72.7% of the vote, the county's highest vote percentage for any presidential candidate since Wyoming statehood in 1890.

United States presidential election results for Natrona County, Wyoming

Year	Republican		Democratic		Third party(ies)
	No.	%	No.	%	No.	%
2024	24,671	72.73%	8,337	24.58%	913	2.69%
2020	25,271	71.79%	8,530	24.23%	1,401	3.98%
2016	23,552	70.62%	6,577	19.72%	3,219	9.65%
2012	22,132	68.37%	8,961	27.68%	1,280	3.95%
2008	21,906	65.85%	10,475	31.49%	886	2.66%
2004	21,512	67.08%	9,863	30.76%	693	2.16%
2000	18,439	64.95%	8,646	30.46%	1,303	4.59%
1996	13,182	46.72%	11,240	39.84%	3,793	13.44%
1992	9,717	35.46%	9,817	35.83%	7,866	28.71%
1988	14,005	59.63%	9,148	38.95%	334	1.42%
1984	18,488	69.86%	7,598	28.71%	378	1.43%
1980	16,801	62.99%	7,111	26.66%	2,760	10.35%
1976	13,761	60.83%	8,640	38.19%	220	0.97%
1972	15,649	70.49%	6,514	29.34%	37	0.17%
1968	10,679	57.19%	5,900	31.59%	2,095	11.22%
1964	10,135	47.58%	11,167	52.42%	0	0.00%
1960	11,809	56.74%	9,002	43.26%	0	0.00%
1956	10,796	62.56%	6,462	37.44%	0	0.00%
1952	10,663	63.87%	6,021	36.06%	11	0.07%
1948	5,341	46.01%	6,183	53.26%	84	0.72%
1944	5,196	51.52%	4,890	48.48%	0	0.00%
1940	5,555	46.49%	6,373	53.34%	21	0.18%
1936	3,810	32.00%	7,819	65.67%	278	2.33%
1932	4,368	37.87%	6,777	58.76%	388	3.36%
1928	7,141	64.78%	3,818	34.64%	64	0.58%
1924	8,267	60.10%	1,631	11.86%	3,857	28.04%
1920	2,957	66.20%	1,153	25.81%	357	7.99%
1916	912	39.19%	1,377	59.17%	38	1.63%
1912	640	45.52%	447	31.79%	319	22.69%
1908	835	63.74%	461	35.19%	14	1.07%
1904	738	69.30%	320	30.05%	7	0.66%
1900	520	66.07%	267	33.93%	0	0.00%
1896	392	54.29%	327	45.29%	3	0.42%
1892	194	55.91%	0	0.00%	153	44.09%

Natrona County is governed by a commission, based in the county seat of Casper. The five-member board consists of commissioners, elected to staggered four-year terms. Current commissioners are:

• Forrest Chadwick (chairman) – Republican
• John Lawson (Vice-chairman) – Republican
• Matt Keating – Republican
• Rob Hendry – Republican
• Steve Schlager – Republican

Natrona County School District Number 1 is the school district for the entire county.

• National Register of Historic Places listings in Natrona County, Wyoming
• Wyoming
  • List of cities and towns in Wyoming
  • List of counties in Wyoming
  • Wyoming statistical areas

• Official website

42°58′N 106°48′W / 42.97°N 106.80°W / 42.97; -106.80