Acton is bounded on the north by Newfield, on the east by Shapleigh, on the south by Lebanon, and on the west by the towns of Wakefield and Milton Mills, NH. It is 85 miles from Boston and 105 miles from Maine's capital, Augusta.

Acton is well watered, having within it's borders more fresh water than any other town in the county. Great East is partly in New Hampshire and extends three miles across the north end of the town. Mousam Lake extends three miles along the eastern line. Square Pond is partly in Shapleigh and is between Great East and Mousam. Wilson has an area of 640 acres and is located one third of a mile from Great East. Horn Pond, one half mile to the eastm is the source of the Salmon Falls River. Balch Pond forms two miles of the northern boundary. Loon Pond is west of Mousam and flows into Lower Mousam. Three smaller ponds, Hansen, Moose, and Swan are in the north end of the town, and Black Pond in the South