Lake Francis Case is a large reservoir impounded by Fort Randall Dam on the Missouri River in south-central South Dakota, United States.

[1] The lake is the eleventh-largest reservoir in the United States and is located within the counties of: Charles Mix, Gregory, Lyman, Brule, and Buffalo.

[4] The resulting reservoir, Lake Francis Case, flooded White Swan, a Native American settlement that had existed along the river.

[6] Species of fish in the reservoir include walleye, northern pike, sauger, sunfish, yellow perch, common carp, black bullhead, channel catfish, and smallmouth bass.

The Karl E. Mundt National Wildlife Refuge is located just downstream of the lake, as a sanctuary for wintering bald eagles.