Dedham , town (1990 pop. 23,782), seat of Norfolk co., E Mass., on the Charles River, a suburb of Boston; inc. 1636. Primarily residential, the town has some light manufacturing. America's oldest frame house, the Fairbanks house (1636), is in Dedham, which is said to have had the first public school in America (1649). The county courthouse was the scene of the Sacco-Vanzetti trial (1921). Horace Mann practiced law in Dedham, and Fisher Ames was born there.