Dexter Reservoir is a reservoir in Lane County, in the U.S. state of Oregon. It is about 16 miles (26 km) southeast of Eugene on the Middle Fork Willamette River, immediately downriver from Lookout Point Lake, another reservoir. The communities of Dexter and Lowell are near the lake. Oregon Route 58 follows the lake's southern shore, while Pengra Road parallels the lake's northern shore as far east as Lowell.

The Middle Fork Willamette River is one of several forks that unite to form the Willamette River in the western part of the U.S. state of Oregon. It is approximately 115 miles (185 km) long, draining an area of the Cascade Range southeast of Eugene, which is at the southern end of the Willamette Valley.