Catonsville is a census-designated place (CDP) in Baltimore County, Maryland. The population was 44,701 at the 2020 US Census. The community is a streetcar suburb of Baltimore along the city's western border. The town is known for its proximity to the Patapsco River and Patapsco Valley State Park, making it a regional mountain biking hub. The town is also notable as a local hotbed of music, earning it the official nickname of "Music City, Maryland." Catonsville contains the majority of the University of Maryland, Baltimore County (UMBC), a major public research university with close to 14,000 students.

The Patapsco River mainstem is a 39-mile (63 km) river in central Maryland that flows into the Chesapeake Bay. The river's tidal portion forms the harbor for the city of Baltimore. With its South Branch, the Patapsco forms the northern border of Howard County, Maryland. The name "Patapsco" is derived from the Algonquian pota-psk-ut, which translates to "backwater" or "tide covered with froth".