Dexter is located at 45°1'24" North, 69°17'24" West (45.023611, -69.290000).
According to the United States Census Bureau, the town has a total area of 5.34 mi2 (13.84 km2). 4.76 mi2 (12.33 km2) of it is land and 0.58 mi2 (1.51 km2) of it is covered by water. The total area is 10.92% water.
Dexter is located in the Eastern Standard Time (EST) timezone, GMT-05:00. It observes Daylight Saving Time (DST).