Great Gunpowder River

Gunpowder River
Gunpowder River travelling through Loch Raven Reservoir in Towson, Maryland
Country	United States
State	Maryland
Tributaries
- left	Little Gunpowder Falls
- right	Big Gunpowder Falls
Cities	Middle River, Joppatowne, Towson, Cockeysville, Parkton, Lineboro
Source
- location	Glen Rock, Pennsylvania
Mouth	Chesapeake Bay
- elevation	0 ft (0 m)

The Gunpowder River is a 6.8-mile-long (10.9 km) tidal inlet on the western side of Chesapeake Bay in Maryland, United States. It is formed by the joining of two freshwater rivers, Gunpowder Falls (often referred to locally as "Big Gunpowder Falls") and Little Gunpowder Falls.

The Big Gunpowder, 56.7 miles (91.2 km) long, begins in the extreme southern part of Pennsylvania's York County. From there, the Gunpowder flows in a generally southeast direction through the length of Baltimore County – past the Perry Hall Mansion and the site of its former plantation – until it reaches Joppatowne where it is joined by the Little Gunpowder and the Bird River, becoming simply the "Gunpowder River" once it passes the Amtrak train bridge that runs from Chase to Joppa. Joppa was an important deep-water seaport and rival to the port of Baltimore in colonial American times, until sedimentation of the Gunpowder River caused by upstream development made its harbor inaccessible to large ships.

Little Gunpowder Falls, as its name implies, is much smaller than the mainstem Gunpowder Falls. Throughout its 25.2-mile (40.6 km) length, it forms much of the boundary between eastern Baltimore County and western Harford County until it reaches the Big Gunpowder. The headquarters of the Gunpowder Falls State Park is located in Harford County along the bank of the Little Gunpowder Falls, in the historic Jerusalem Mill Village. The remainder of the boundary between Baltimore and Harford counties is formed by the Gunpowder River, the tidal estuary of the Chesapeake Bay formed by the union of Little Gunpowder Falls and the Gunpowder Falls rivers.