Riley's Lock (Lock 24) and lock house are part of the 184.5-mile (296.9 km) Chesapeake and Ohio Canal (a.k.a. C&O Canal) that operated in the United States along the Potomac River from the 1830s through 1923. They are located at towpath mile-marker 22.7 adjacent to Seneca Creek, in Montgomery County, Maryland. The lock is sometimes identified as Seneca because of the Seneca Aqueduct that carried the canal over the creek to the lift lock. The name Riley comes from John C. Riley, who was lock keeper from 1892 until the canal closed permanently in 1924.