Cottage Grove Lake is a reservoir on the Coast Fork Willamette River in Lane County, Oregon, United States. The lake is about 3 miles (4.8 km) long.

Cottage Grove Dam, which impounds the lake, is 1,750 feet (530 m) long and 95 feet (29 m) high. It was completed in 1942 as one of the 13 dams built by the United States Army Corps of Engineers in the Willamette River basin. It is about 5 miles (8 km) south of Cottage Grove at river mile 29 (kilometer 47).

The dam's main function, in conjunction with the Dorena Dam on the Row River, a Coast Willamette tributary, is flood control. Other functions are to supply water for irrigation and improved river navigation. The lake and its surrounds are used for recreation, including boating, camping, fishing, picnicking, and bird-watching.

• List of lakes in Oregon