Location
The Sugarland Run and Horsepen Creek watersheds (22.5 square miles and 23.5 square miles, respectively) are located in the northwestern part of Fairfax County, and cross into Loudoun County. Sugarland Run drains to the Potomac River and Horsepen Creek drains into South Fork Broad Run, which then drains into the Potomac River.

Major Streams and Tributaries
Sugarland Run: Major tributaries include Folly Lick Branch, Offuts Branch and Rosiers Branch, as well as some unnamed streams.
Horsepen Creek: Major tributaries include Cedar Run and Frying Pan Branch as well as some unnamed streams.

Unique Features
The town of Herndon is on the border between the two watersheds. Part of the Dulles Airport property is in the Horsepen Creek watershed and Frying Pan Park is also in this watershed.