| Piney Run | |
| Subdivision Type1: | Country |
| Subdivision Name1: | United States |
| Subdivision Type2: | State |
| Subdivision Name2: | Virginia |
| Subdivision Type3: | Region |
| Subdivision Name3: | Loudoun County |
| Length: | 9miles |
| Source1 Location: | Neersville |
| Source1 Coordinates: | 39.24°N -77.74°W |
| Source1 Elevation: | 650feet |
| Mouth: | Potomac River |
| Mouth Location: | Loudoun Heights |
| Mouth Coordinates: | 39.32°N -77.71°W |
| Mouth Elevation: | 240feet |
| Basin Size: | 15.2sqmi |
| Tributaries Left: | Sweet Run |
Piney Run is a tributary of the Potomac River in Loudoun County, Virginia. The creek is the principal drainage of the upper Between the Hills valley in northwestern Loudoun County.
The headwaters of the creek are located approximately 1.75miles south of Neersville, Virginia, just west of State Route 671 (Harpers Ferry Road). Just prior to an impoundment, 5miles from its headwaters in Sweet Run State Park, the creek is joined by its only named tributary branch, Sweet Run. From the impoundment, the creek flows 2miles, to the crossing by State Route 671, whereupon the creek cuts a deep gorge, falling 150feet over its last 2miles. Just prior to its confluence with the Potomac below the White Horse Rapids, 4500feet down river from the confluence with the Shenandoah River, the creek passes through a culvert under U.S. Route 340 and then cascades approximately 20feet over a waterfall, the only in Loudoun County.