Adjacent counties

• Lincoln County – west
• Waldo County – north
• Hancock County – northeast

National protected areas

• Franklin Island National Wildlife Refuge
• Seal Island National Wildlife Refuge

2000 census

At the 2000 census there were 39,618 people, 16,608 households, and 10,728 families living in the county. The population density was 108 people per square mile (42 people/km²). There were 21,612 housing units at an average density of 59 per square mile (23/km²). The racial makeup of the county was 98.28% White, 0.24% Black or African American, 0.22% Native American, 0.36% Asian, 0.01% Pacific Islander, 0.12% from other races, and 0.78% from two or more races. 0.57% of the population were Hispanic or Latino of any race. 25.4% were of English, 12.2% Irish, 11.7% United States or American, 7.5% German and 5.7% French ancestry. 97.1% spoke English and 1.5% French as their first language.^[12] Of the 16,608 households 28.30% had children under the age of 18 living with them, 52.20% were married couples living together, 9.00% had a female householder with no husband present, and 35.40% were non-families. 29.00% of households were one person and 12.70% were one person aged 65 or older. The average household size was 2.31 and the average family size was 2.83.

The age distribution was 22.40% under the age of 18, 6.30% from 18 to 24, 27.40% from 25 to 44, 26.70% from 45 to 64, and 17.20% 65 or older. The median age was 41 years. For every 100 females there were 95.20 males. For every 100 females age 18 and over, there were 93.00 males.

The median household income was $36,774 and the median family income was $43,819. Males had a median income of $30,704 versus $22,382 for females. The per capita income for the county was $19,981. About 6.40% of families and 10.10% of the population were below the poverty line, including 11.90% of those under age 18 and 8.00% of those age 65 or over.

2010 census

At the 2010 census, there were 39,736 people, 17,258 households, and 10,662 families living in the county.^[13] The population density was 108.8 inhabitants per square mile (42.0/km²). There were 23,744 housing units at an average density of 65.0 units per square mile (25.1 units/km²).^[14] The racial makeup of the county was 97.1% white, 0.5% black or African American, 0.5% Asian, 0.4% American Indian, 0.2% from other races, and 1.4% from two or more races. Those of Hispanic or Latino origin made up 0.8% of the population.^[13] In terms of ancestry, 31.3% were English, 19.0% were Irish, 12.8% were German, 6.9% were Scottish, and 5.9% were American.^[15]

Of the 17,258 households, 25.4% had children under the age of 18 living with them, 48.2% were married couples living together, 9.4% had a female householder with no husband present, 38.2% were non-families, and 31.0% of households were made up of individuals. The average household size was 2.22 and the average family size was 2.75. The median age was 46.2 years.^[13]

The median household income was $45,264 and the median family income was $55,830. Males had a median income of $40,712 versus $29,732 for females. The per capita income for the county was $25,291. About 7.9% of families and 12.5% of the population were below the poverty line, including 16.5% of those under age 18 and 9.8% of those age 65 or over.^[16]

Voter registration

City

• Rockland (county seat)

Towns

Plantation

• Matinicus Isle

Unorganized territories

• Criehaven
• Muscle Ridge Islands

Census-designated places

• Camden
• Thomaston

Other unincorporated villages

• Glen Cove
• Hibberts Corner
• Port Clyde
• West Rockport