Farmers found the surface of the town uneven, its hard and rocky soil "tolerably productive." Outlets of ponds, however, provided Casco with good sites for water powered mills. The town had 4 sawmills, 4 gristmills, a shook mill, a barrel stave mill, 4 shingle factories, a carriage factory and a tannery. In 1832, the Cumberland and Oxford Canal made Sebago Lake a direct trade route to Portland. Steamboat travel commenced on the waterways in the 1840s, carrying tourists and freight. In 1938, Sebago Lake State Park was established, one of the state's 5 original state parks.
As of the census of 2000, there were 3,469 people, 1,327 households, and 958 families residing in the town. The population density was 110.9 people per square mile (42.8/km²). There were 1,958 housing units at an average density of 62.6/sq mi (24.2/km²). The racial makeup of the town was 97.95% White, 0.29% African American, 0.37% Native American, 0.52% Asian, 0.12% from other races, and 0.75% from two or more races. Hispanic or Latino of any race were 0.52% of the population.
There were 1,327 households out of which 34.1% had children under the age of 18 living with them, 58.3% were married couples living together, 10.4% had a female householder with no husband present, and 27.8% were non-families. 20.4% of all households were made up of individuals and 6.8% had someone living alone who was 65 years of age or older. The average household size was 2.58 and the average family size was 2.96.
In the town the population was spread out with 25.2% under the age of 18, 6.5% from 18 to 24, 32.1% from 25 to 44, 24.7% from 45 to 64, and 11.4% who were 65 years of age or older. The median age was 38 years. For every 100 females there were 97.7 males. For every 100 females age 18 and over, there were 94.3 males.
The median income for a household in the town was $41,629, and the median income for a family was $49,500. Males had a median income of $31,679 versus $25,306 for females. The per capita income for the town was $19,306. About 5.3% of families and 8.1% of the population were below the poverty line, including 8.5% of those under age 18 and 9.8% of those age 65 or over.