Geography Facts About the U.S. Counties

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In the United States, a county is an administrative and political subdivision of U.S. states. The United States Census Bureau uses county equivalent to represent places similar to counties but called various names (parishes in Louisiana, boroughs in Alaska).

The specific governmental powers of counties vary widely between the states. Counties have significant functions in all states except Rhode Island and Connecticut, where county governments have been abolished, but the entities remain administrative or statistical.

There are nowadays 3,143 counties and county-equivalents in the 50 U.S. states and D.C. The quantity of U.S. counties per state varies from the three counties of Delaware to the 254 counties of Texas.

The History of U.S Counties

The first U.S. county (James City in Virginia) was founded in 1634. The map below shows when was each U.S. county and county-equivalents created.

Some established counties haven’t existed long. For example, Bullfrog County in Nevada was founded in 1987 and abolished just two years later. The latest U.S. county, Broomfield Country, was organized in Colorado in 2001.

The animated map below shows the territorial evolution of U.S. counties and their borders.

Largest and smallest counties by land area

The state’s largest county-equivalent by area is the Yukon–Koyukuk Census Area (145.50 thousand sq mi or 376.86 thousand sq km). It is the only administrative or political subdivision that is larger than the entire state of Montana.

The map below shows U.S. Counties Bigger than States.

Largest counties and county-equivalents by land area

Rank	County	State	Area (sq mi)	Area (sq km)
1	Yukon-Koyukuk	Alaska	145,899.69	377,868.50
2	North Slope	Alaska	88,817.12	230,035.30
3	Bethel	Alaska	40,633.31	105,239.80
4	Northwest Arctic	Alaska	35,898.34	92,976.30
5	Valdez-Cordova	Alaska	34,319.10	88,886
6	Southeast Fairbanks	Alaska	24,814.86	64,270.20
7	Matanuska-Susitna	Alaska	24,681.54	63,924.90
8	Lake and Peninsula	Alaska	23,781.96	61,595.0 0
9	Nome	Alaska	23,000.91	59,572
10	San Bernardino	California	20,052.5	51,936

The map below created by Jerry Brekhus shows the largest county In each U.S. state.

The smallest counties by land area

The smallest county by area is Nevada, with 11.99 sq mi or 31.05 sq km.

Rank	County	State	Area (sq mi)	Area (sq km)
1	Kalawao	Hawaii	11.99	31.05
2	New York	New York	22.83	59.13
3	Bristol	Rhode Island	24.16	62.57
4	Arlington	Virginia	25.97	67.26
5	Broomfield	Colorado	33.03	85.55
6	Bronx	New York	42.10	109.04
7	Nantucket	Massachusetts	44.97	116.47
8	Hudson	New Jersey	46.19	119.63
9	San Francisco	California	46.87	121.39
10	Suffolk	Massachusetts	58.15	150.61

U.S. Counties With More than 1 Million People

Forty-three counties in the U.S. have a population greater than one million.

Population density

County populations vary broadly. According to the Census Bureau, more than 50% of the U.S. population is concentrated in just 143 counties (4.6% of all U.S. counties). The 5 most populous counties are Los Angeles County (California), Cook County (Illinois), Harris County (Texas), Maricopa County (Arizona), and San Diego County (California).

The largest population has Los Angeles County, where live more than 10 million people. New York is the most densely populated county in the United States (69,468 pop/sq mi or 26,822 Pop/sq km).

Most densely populated counties

Rank	County	State	Pop/sq mi	Pop/sq km
1	New York	New York	69,468	26,822
2	Kings	New York	35,369	13,656
3	Bronx	New York	32,903	12,704
4	Queens	New York	20,554	7,936
5	San Francisco	California	17,179	6,633
6	Hudson	New York	13,732	5,302
7	Suffolk	New Jersey	12,417	4,794
8	Philadelphia	Pennsylvania	11,379	4,394
9	Washington	D.C.	9,857	3,806
10	Alexandria	Virginia	9,314	3,596

It is to be expected that Yukon–Koyukuk Census Area in Alaska has the lowest population density.

Least densely populated counties

Rank	County	State	Pop/sq mi	Pop/sq km
1	Yukon–Koyukuk	Alaska	0.03	0.01
2	Lake and Peninsula	Alaska	0.06	0.02
3	Yakutat	Alaska	0.08	0.03
4	North Slope	Alaska	0.10	0.04
5	Loving	Texas	0.12	0.04
6	Denali	Alaska	0.14	0.05
7	Northwest Arctic	Alaska	0.21	0.08
8	Esmeralda	Nevada	0.21	0.08
9	Garfield	Montana	0.25	0.10
10	Dillingham	Alaska	0.26	0.10

More than half of all American residents live in just 143 big U.S. counties.

The shape of U.S. counties

One of the most interesting facts is that 414 American states are rectangular. Most of them are located in the Midwest. The map below shows all rectangular counties in the United States.

These counties have rectangular or square shapes because there aren’t sufficient natural barriers like rivers or lakes, so lines of latitude and longitude are used to mark borders.

Top U.S. states by number rectangular or square counties

Texas: 87
Kansas: 73
Iowa: 59
Nebraska: 46
Illinois: 19
South Dakota: 19
Missouri: 16
Minnesota: 15
Oklahoma: 13
Wisconsin: 11
Mississippi: 10
Colorado: 8
North Dakota: 8
Ohio: 7
Wyoming: 7
North Carolina: 6
Alabama: 3
Kentucky: 3
Florida: 2
Arizona: 1
New York: 1

The most unusually shaped counties have prominent geographical features, either bordering a body of water or having mountains, etc. For instance, below is the map of Monroe County in Florida.