The town center, where over 50% of the population resides, is defined as the Peterborough census-designated place (CDP), and is located near the intersection of U.S. Route 202 and New Hampshire Route 101 along the Contoocook River.
According to the United States Census Bureau, the town has a total area of 38.1 square miles (99 kmē), of which 37.7 sq mi (98 kmē) is land and 0.4 sq mi (1.0 kmē) is water, comprising 1.08% of the town. The highest point in Peterborough is South Pack Monadnock Mountain (2,290 feet (698 m) above sea level), in Miller State Park.
The town center, or census-designated place, has a total area of 4.8 square miles (12.4 kmē), of which 4.7 sq mi (12.2 kmē) is land and 0.04 sq mi (0.1 kmē) (0.42%) is water.





