Dummer is a town in Coos County. Dummer is home to the Pontook Reservoir, popular with canoeists, kayakers and birdwatchers. In the western part of Dummer lies the village of Paris.

The town has a total area of 49.5 square miles. The highest point in Dummer is the summit of Cow Mountain, at 2,289 feet above sea level. Roughly the western third of Dummer lies within the Connecticut River watershed, where it is drained by the Upper Ammonoosuc River, with the eastern two-thirds in the Androscoggin River watershed. The former community of Paris is in the western part of town, along Phillips Brook.

Dummer is bordered by Milan to the south, Errol and Millsfield to the north, Cambridge to the east, and Odell and Stark to the west.

Dummer is crossed by NH-16.