Guernsey County is a county located in the U.S. state of Ohio. As of the 2020 census, the population was 38,438. Its county seat and largest city is Cambridge. It is named for the Isle of Guernsey in the English Channel, from which many of the county's early settlers emigrated.

Guernsey County comprises the Cambridge, OH Micropolitan Statistical Area, which is also included in the Columbus-Marion-Zanesville, OH Combined Statistical Area.

Guernsey County, located in the Appalachian foothills, was first formed and organized on March 10, 1810, from portions of Muskingum and Belmont counties, after the Ohio Legislature acted. The first county commissioners were sworn in on April 23, 1810. It lost some land area during the formation of neighboring counties until it reached its present boundaries in 1851, after Buffalo, Beaver, Olive, and Seneca townships were gained by Noble county. After dispute whether the county seat should be established in Cambridge or Washington, it was established in Cambridge after two individuals proposed to donate the land and furnish the public buildings if built in Cambridge.

According to the U.S. Census Bureau, the county has a total area of 528 square miles (1,370 km), of which 522 square miles (1,350 km) is land and 6.0 square miles (16 km) (1.1%) is water.

Historical population

Census	Pop.	Note	%±
1810	3,051		—
1820	9,292		204.6%
1830	18,036		94.1%
1840	27,748		53.8%
1850	30,438		9.7%
1860	24,474		−19.6%
1870	23,838		−2.6%
1880	27,197		14.1%
1890	28,645		5.3%
1900	34,425		20.2%
1910	42,716		24.1%
1920	45,352		6.2%
1930	41,486		−8.5%
1940	38,822		−6.4%
1950	38,452		−1.0%
1960	38,579		0.3%
1970	37,665		−2.4%
1980	42,024		11.6%
1990	39,024		−7.1%
2000	40,792		4.5%
2010	40,087		−1.7%
2020	38,438		−4.1%
U.S. Decennial Census 1790-1960 1900-1990 1990-2000 2020

As of the census of 2000, there were 40,792 people, 16,094 households, and 11,233 families living in the county. The population density was 78 inhabitants per square mile (30/km). There were 18,771 housing units at an average density of 36 units per square mile (14/km). The racial makeup of the county was 96.28% White, 1.53% Black or African American, 0.31% Native American, 0.30% Asian, 0.22% from other races, and 1.36% from two or more races. 0.62% of the population were Hispanic or Latino of any race. 96.7% spoke English, 1.3% Spanish and 1.1% German as their first language.

There were 16,094 households, out of which 32.40% had children under the age of 18 living with them, 53.90% were married couples living together, 11.40% had a female householder with no husband present, and 30.20% were non-families. 26.10% of all households were made up of individuals, and 11.20% had someone living alone who was 65 years of age or older. The average household size was 2.50 and the average family size was 3.00.

In the county, the population was spread out, with 26.20% under the age of 18, 7.90% from 18 to 24, 27.50% from 25 to 44, 24.00% from 45 to 64, and 14.50% who were 65 years of age or older. The median age was 38 years. For every 100 females there were 94.50 males. For every 100 females age 18 and over, there were 91.40 males.

The median income for a household in the county was $30,110, and the median income for a family was $35,660. Males had a median income of $30,142 versus $20,804 for females. The per capita income for the county was $15,542. About 12.90% of families and 16.00% of the population were below the poverty line, including 21.50% of those under age 18 and 12.30% of those age 65 or over.

As of the 2010 United States Census, there were 40,087 people, 16,210 households, and 10,949 families living in the county. The population density was 76.8 inhabitants per square mile (29.7/km). There were 19,193 housing units at an average density of 36.8 units per square mile (14.2 units/km). The racial makeup of the county was 96.0% white, 1.5% black or African American, 0.3% Asian, 0.2% American Indian, 0.2% from other races, and 1.8% from two or more races. Those of Hispanic or Latino origin made up 0.9% of the population. In terms of ancestry, 22.3% were German, 15.2% were Irish, 12.4% were English, and 9.6% were American.

Of the 16,210 households, 31.1% had children under the age of 18 living with them, 49.8% were married couples living together, 12.3% had a female householder with no husband present, 32.5% were non-families, and 27.7% of all households were made up of individuals. The average household size was 2.44 and the average family size was 2.95. The median age was 40.9 years.

The median income for a household in the county was $37,573 and the median income for a family was $48,445. Males had a median income of $37,642 versus $29,348 for females. The per capita income for the county was $19,187. About 13.6% of families and 17.3% of the population were below the poverty line, including 26.7% of those under age 18 and 9.5% of those age 65 or over.

Guernsey County has been dominated by Republican Party candidates in presidential elections, with Democrats only winning the county in six presidential elections from 1856 on. The most recent of these Democrats to win the county was Bill Clinton in 1996.

United States presidential election results for Guernsey County, Ohio

Year	Republican		Democratic		Third party(ies)
	No.	%	No.	%	No.	%
2020	13,407	73.41%	4,577	25.06%	280	1.53%
2016	11,445	68.75%	4,359	26.18%	843	5.06%
2012	8,993	53.37%	7,450	44.22%	406	2.41%
2008	9,197	52.93%	7,625	43.88%	553	3.18%
2004	9,962	55.84%	7,768	43.54%	110	0.62%
2000	8,181	53.02%	6,643	43.05%	606	3.93%
1996	5,970	39.52%	6,731	44.55%	2,407	15.93%
1992	5,749	35.17%	6,428	39.32%	4,171	25.51%
1988	8,507	58.42%	5,926	40.69%	130	0.89%
1984	10,252	66.81%	4,967	32.37%	125	0.81%
1980	8,180	58.08%	5,121	36.36%	783	5.56%
1976	7,746	49.90%	7,573	48.78%	205	1.32%
1972	9,648	66.00%	4,757	32.54%	214	1.46%
1968	7,336	49.44%	5,815	39.19%	1,686	11.36%
1964	6,429	40.35%	9,503	59.65%	0	0.00%
1960	10,396	61.41%	6,532	38.59%	0	0.00%
1956	10,224	66.51%	5,149	33.49%	0	0.00%
1952	9,749	59.52%	6,631	40.48%	0	0.00%
1948	7,651	53.21%	6,639	46.17%	90	0.63%
1944	8,878	57.69%	6,512	42.31%	0	0.00%
1940	10,125	53.76%	8,710	46.24%	0	0.00%
1936	8,532	42.51%	11,404	56.82%	134	0.67%
1932	8,750	48.33%	9,026	49.85%	330	1.82%
1928	11,174	74.10%	3,709	24.60%	197	1.31%
1924	8,997	59.56%	3,604	23.86%	2,505	16.58%
1920	8,764	54.36%	6,888	42.72%	470	2.92%
1916	4,228	44.76%	4,312	45.65%	906	9.59%
1912	3,426	37.68%	2,726	29.98%	2,940	32.34%
1908	5,210	53.92%	3,449	35.69%	1,004	10.39%
1904	5,427	62.89%	2,448	28.37%	755	8.75%
1900	5,014	59.44%	3,120	36.99%	301	3.57%
1896	4,337	55.78%	3,258	41.90%	180	2.32%
1892	3,439	53.53%	2,510	39.07%	476	7.41%
1888	3,560	54.40%	2,520	38.51%	464	7.09%
1884	3,409	55.18%	2,570	41.60%	199	3.22%
1880	3,318	55.78%	2,568	43.17%	62	1.04%
1876	3,106	55.60%	2,460	44.04%	20	0.36%
1872	2,629	57.78%	1,901	41.78%	20	0.44%
1868	2,743	58.46%	1,949	41.54%	0	0.00%
1864	2,677	57.52%	1,977	42.48%	0	0.00%
1860	2,510	55.18%	1,933	42.49%	106	2.33%
1856	2,392	52.76%	1,932	42.61%	210	4.63%

• Cambridge (county seat)

• Buffalo
• Kimbolton
• Salesville

• Antrim
• Birmingham
• Claysville
• Derwent
• Elizabethtown
• Guernsey
• Kings Mine
• Kipling
• Opperman
• Walhonding

• Big Muskie
• Guernsey County Courthouse
• National Register of Historic Places listings in Guernsey County, Ohio

• Thomas William Lewis, History of Southeastern Ohio and the Muskingum Valley, 1788-1928. In Three Volumes. Chicago: S.J. Clarke Publishing Co., 1928.

• Official Guernsey County website

40°03′N 81°30′W / 40.05°N 81.50°W / 40.05; -81.50