At its founding, Lincoln County accounted for three-fifths of the state's land, and stretched east to Nova Scotia. Thirteen counties were cut out of this land including Sagadahoc County to the west. The county flag is a traditional New England flag, adopted in 1977.
According to the U.S. Census Bureau, the county has a total area of 700 square miles (1,800 km2), of which 456 square miles (1,180 km2) is land and 244 square miles (630 km2) (35%) is water. It is the third-smallest county in Maine by area.
As of the census of 2010, there were 34,457 people. As of 2000, there were 14,158 households, and 9,542 families residing in the county. The population density was 74 people per square mile (28/km²). There were 20,849 housing units at an average density of 46 per square mile (18/km²). The racial makeup of the county was 98.46% White, 0.17% Black or African American, 0.26% Native American, 0.37% Asian, 0.02% Pacific Islander, 0.10% from other races, and 0.61% from two or more races. 0.46% of the population were Hispanic or Latino of any race. 25.3% were of English, 15.4% United States or American, 11.2% Irish, 9.0% German and 7.3% French ancestry according to Census 2000. Most of those claiming to be of "American" ancestry are actually of English descent, but have family that has been in the country for so long, in many cases since the early seventeenth century that they choose to identify simply as "American". 97.7% spoke English and 1.0% French as their first language.
There were 14,158 households out of which 28.20% had children under the age of 18 living with them, 56.10% were married couples living together, 7.70% had a female householder with no husband present, and 32.60% were non-families. 26.70% of all households were made up of individuals and 12.10% had someone living alone who was 65 years of age or older. The average household size was 2.35 and the average family size was 2.82.
In the county the population was spread out with 22.70% under the age of 18, 5.50% from 18 to 24, 25.60% from 25 to 44, 28.10% from 45 to 64, and 18.20% who were 65 years of age or older. The median age was 43 years. For every 100 females there were 95.10 males. For every 100 females age 18 and over, there were 92.00 males.
The median income for a household in the county was $38,686, and the median income for a family was $45,427. Males had a median income of $31,209 versus $23,161 for females. The per capita income for the county was $20,760. About 6.60% of families and 10.10% of the population were below the poverty line, including 12.80% of those under age 18 and 9.50% of those age 65 or over.
^Reynolds Farley, 'The New Census Question about Ancestry: What Did It Tell Us?', Demography, Vol. 28, No. 3 (August 1991), pp. 414, 421.
^Stanley Lieberson and Lawrence Santi, 'The Use of Nativity Data to Estimate Ethnic Characteristics and Patterns', Social Science Research, Vol. 14, No. 1 (1985), pp. 44–6.
^Stanley Lieberson and Mary C. Waters, 'Ethnic Groups in Flux: The Changing Ethnic Responses of American Whites', Annals of the American Academy of Political and Social Science, Vol. 487, No. 79 (September 1986), pp. 82–86.
^Mary C. Waters, Ethnic Options: Choosing Identities in America (Berkeley: University of California Press, 1990), p. 36.