Geography - According to the United States Census Bureau, the town has a total area of 35.0 square miles, of which, 34.4 square miles of it is land and 0.5 square miles of it (1.52%) is water. The town is bordered by the towns of North Salem and Lewisboro in Westchester County, New York to the west, Danbury, Connecticut to the north, Wilton, Connecticut to the south and Redding, Connecticut to the east.

The town has a Metro North railroad station called "Branchville." Branchville is a business and residential community in the southeast corner of the town.

Demographics - As of the census of 2000, there were 23,643 people, 8,433 households, and 6,611 families residing in the town. The population density was 686.7 people per square mile. There were 8,877 housing units at an average density of 257.8/sq mi. The racial makeup of the town was 96.12% White, 0.62% Black or African American, 0.09% Native American, 2.08% Asian, 0.03% Pacific Islander, 0.36% from other races, and 0.70% from two or more races. Hispanic or Latino of any race were 1.97% of the population.

There were 8,433 households out of which 43.0% had children under the age of 18 living with them, 70.6% were married couples living together, 6.0% had a female householder with no husband present, and 21.6% were non-families. 18.9% of all households were made up of individuals and 7.5% had someone living alone who was 65 years of age or older. The average household size was 2.78 and the average family size was 3.21.

In the town the population was spread out with 30.6% under the age of 18, 3.2% from 18 to 24, 27.8% from 25 to 44, 27.5% from 45 to 64, and 10.9% who were 65 years of age or older. The median age was 39 years. For every 100 females there were 92.8 males. For every 100 females age 18 and over, there were 89.4 males.

The median income for a household in the town was $107,351, and the median income for a family was $127,981. Males had a median income of $100,000 versus $50,236 for females. The per capita income for the town was $51,795. About 1.3% of families and 2.4% of the population were below the poverty line, including 1.7% of those under age 18 and 5.3% of those age 65 or over.

The median income for a household in the CDP is $81,179, and the median income for a family is $127,327. Males have a median income of $93,084 versus $47,232 for females. The per capita income for the CDP is $46,843. 3.2% of the population and 1.7% of families are below the poverty line. Out of the total population, 1.6% of those under the age of 18 and 6.8% of those 65 and older are living below the poverty line.