2000 census

As of the census^[11] 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/km²). There were 18,771 housing units at an average density of 36 units per square mile (14/km²). 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.

2010 census

As of the 2010 United States Census, there were 40,087 people, 16,210 households, and 10,949 families living in the county.^[12] The population density was 76.8 inhabitants per square mile (29.7/km²). There were 19,193 housing units at an average density of 36.8 units per square mile (14.2 units/km²).^[13] 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.^[12] In terms of ancestry, 22.3% were German, 15.2% were Irish, 12.4% were English, and 9.6% were American.^[14]

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.^[12]

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.^[15]

City

• Cambridge (county seat)

Villages

Townships

^[17]

Census-designated places

• Buffalo
• Kimbolton
• Salesville

Unincorporated communities

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