Mare Cognitum (the "sea that has become known") is a lunar mare located in a basin or large crater which sits in the second ring of the Procellarum basin. The basin material is of the Lower Imbrian epoch, while the basaltic mare material is of the Upper Imbrian epoch. To the northwest of the mare is the Montes Riphaeus mountain range, part of the rim of the buried crater or basin containing the mare.

Fra Mauro formation, the landing site of Apollo 14, is located near Mare Cognitum.