Dedham ( DED-əm) is a town in, and the county seat of, Norfolk County, Massachusetts, United States. Located on Boston's southwestern border, the population was 25,364 at the 2020 census.

First settled by English colonists in 1635 and incorporated in 1636, Dedham established the first public school in America in 1643. Dedham is home to the Fairbanks House, the oldest surviving timber-frame house in the United States. On January 1, 1643, by unanimous vote, Dedham authorized the first taxpayer-funded public school, "the seed of American education." The first man-made canal in North America, Mother Brook, was created in Dedham in 1639.

The town took an active part in the American Revolution and was home to the Dedham Liberty Pole in the late 18th century. When a split occurred at the First Church and Parish in Dedham, the resulting lawsuit became known as The Dedham Case, an important landmark in the separation of church and state. In 1921, the historic Sacco and Vanzetti trial was held in the Norfolk County Courthouse. Dedham is sometimes called the "mother of towns" because 14 present-day communities were included within its original broad borders.

Dedham is governed by a representative town meeting, a select board which appoints the town manager, and various other boards and committees. The town is served by the MBTA commuter rail and bus service. The Dedham Public Schools operates seven schools, and a number of private schools also operate within the town.