It was settled in 1635 by people from Roxbury and Watertown and incorporated in 1636 (making it quite old by US standards), and is the county seat of Norfolk County. Its motto (and at one time the name of the town) is "Contentment".
Dedham is home to the Fairbanks House, the oldest wood-frame house in the United States. Other Dedham firsts include the first taxpayer-funded public school in the US and the first man-made canal, the Mother Brook, which linked the Charles River to local mills.
According to the United States Census Bureau, the town has a total area of 27.6 km² (10.6 mi²). 27.1 km² (10.4 mi²) of it is land and 0.5 km² (0.2 mi²) of it is water. The total area is 1.79% water.
As of the census of 2000, there are 23,464 people, 8,654 households, and 6,144 families residing in the town. The population density is 866.9/km² (2,244.6/mi²). There are 8,908 housing units at an average density of 329.1 persons/km² (852.2 persons/mi²). The racial makeup of the town is 94.51% White, 1.54% African American, 0.16% Native American, 1.87% Asian, 0.04% Pacific Islander, 0.80% from other races, and 1.08% from two or more races. 2.42% of the population are Hispanic or Latino of any race.
There are 8,654 households out of which 30.1% have children under the age of 18 living with them, 56.3% are married couples living together, 11.1% have a woman whose husband does not live with her, and 29.0% are non-families. 23.9% of all households are made up of individuals and 10.4% have someone living alone who is 65 years of age or older. The average household size is 2.61 and the average family size is 3.14.
In the town the population is spread out with 22.2% under the age of 18, 5.8% from 18 to 24, 31.1% from 25 to 44, 24.2% from 45 to 64, and 16.6% who are 65 years of age or older. The median age is 40 years. For every 100 females there are 93.4 males. For every 100 females age 18 and over, there are 92.0 males.
The median income for a household in the town is $61,699, and the median income for a family is $72,330. Males have a median income of $46,216 versus $35,682 for females. The per capita income for the town is $28,199. 4.6% of the population and 3.2% of families are below the poverty line. Out of the total people living in poverty, 3.9% are under the age of 18 and 6.5% are 65 or older.