The Ossipee River begins at the village of Effingham Falls, New Hampshire, at the outlet of Berry Bay, the farthest downstream of a chain of lakes connected to
Ossipee Lake. The river, flowing east, forms the border between the towns of
Freedom. Entering Maine, the river continues to serve as a municipal boundary, first between
Parsonsfield, and then between
Kezar Falls, a village in the town of Porter, forms a significant community along the river, with two dam impoundments.