Stillwell Run is a long first-order tributary to the Occoquan River in Fairfax County, Virginia. This is the only stream of this name in the United States.
Stillwell Run rises on the Maple Branch divide and then flows southwesterly to join the Occoquan River about 2.5 miles south-southwest of Makleys Corners.
Stillwell Run drains of area, receives about 43.4 in/year of precipitation, and is about 84.36% forested.