Dedham is located at 42°14'29" North, 71°9'59" West (42.241389, -71.166389).
According to the United States Census Bureau, the town has a total area of 10.64 mi2 (27.57 km2). 10.45 mi2 (27.07 km2) of it is land and 0.19 mi2 (0.50 km2) of it is covered by water. The total area is 1.80% water.
Dedham is located in the Eastern Standard Time (EST) timezone, GMT-05:00. It observes Daylight Saving Time (DST).