The CDP is bordered to the northwest by the Connecticut River, which forms the Vermont state line.

To the north the CDP extends to Baker Pond and the location known as "Coos Junction".

The CDP includes all of Riverside Drive and Hartco Avenue on the southeastern side of the village.

To the west, the CDP extends out Elm Street beyond Blackberry Lane.

Routes 2 and 3 run through the center of Lancaster as Main Street, splitting near the northern and southern ends of the CDP.

New Hampshire Route 135 (Elm Street) leads southwest from Lancaster 19 miles (31 km) to the outskirts of Littleton.