According to the United States Census Bureau, the town has a total area of 109.1 km² (42.1 mi²). 84.4 km² (32.6 mi²) of it is land and 24.8 km² (9.6 mi²) of it is water. The total area is 22.69% water.
As of the census of 2000, there are 12,987 people, 5,290 households, and 3,459 families residing in the town. The population density is 153.9/km² (398.6/mi²). There are 5,601 housing units at an average density of 66.4 persons/km² (171.9 persons/mi²). The racial makeup of the town is 97.60% White, 0.39% African American, 0.08% Native American, 0.80% Asian, 0.01% Pacific Islander, 0.33% from other races, and 0.79% from two or more races. 1.04% of the population are Hispanic or Latino of any race.
There are 5,290 households out of which 30.1% have children under the age of 18 living with them, 54.0% are married couples living together, 8.4% have a woman whose husband does not live with her, and 34.6% are non-families. 28.3% of all households are made up of individuals and 11.7% have someone living alone who is 65 years of age or older. The average household size is 2.42 and the average family size is 3.00.
In the town the population is spread out with 23.0% under the age of 18, 5.1% from 18 to 24, 28.3% from 25 to 44, 28.1% from 45 to 64, and 15.6% who are 65 years of age or older. The median age is 42 years. For every 100 females there are 89.8 males. For every 100 females age 18 and over, there are 86.2 males.
The median income for a household in the town is $57,284, and the median income for a family is $74,931. Males have a median income of $51,408 versus $38,476 for females. The per capita income for the town is $32,516. 7.1% of the population and 4.1% of families are below the poverty line. Out of the total people living in poverty, 7.8% are under the age of 18 and 13.0% are 65 or older.