Catonsville (/ˈkeɪtənzˌvɪl/) 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.

Before European colonists settled in present-day Catonsville, the area was occupied by the Piscataway tribe or the Susquehannocks.

Rolling Road was used to transport tobacco south from plantations to the Patapsco River on horse-drawn wagons.

In 1787, the Ellicott family built the Frederick Turnpike to transport goods from their flour mill, Ellicott Mills, to the Baltimore harbor. Charles Carroll, a signer of the Declaration of Independence, owned the land around the then newly built road. He instructed his son-in-law, Richard Caton, to develop the area along the road. Caton and his wife, Mary Carroll Caton, lived in Castle Thunder, constructed on the Frederick Turnpike in 1787.

Caton gave his name to the community and called it "Catonville," although the name was changed to "Catonsville" in the 1830s. Businesses were built along the Frederick Turnpike for travelers traveling from Ellicott City to Baltimore. Catonsville served as a layover stop for travelers and the town increasingly grew and developed. The pleasant surroundings attracted wealthy Baltimore merchants who built large Victorian and colonial summer homes to escape Baltimore's summer heat. Starting in 1862, horsecar services connected Catonsville to Baltimore. In 1884, the Catonsville Short Line railroad was built, providing 8 roundtrip trains to Baltimore daily. This allowed residents to commute to work in Baltimore. Commuter traffic exploded in the 1890s with the construction of electric streetcar lines and fancy housing developments. Catonsville had become one of the first commuter suburbs in the United States. Baltimore has tried to annex Catonsville, although their attempts have all been failures. The last attempt was in 1918.

Homes of all sizes were constructed rapidly through the 1970s, when much of land around the Frederick Turnpike had been converted into housing. A new and modern business district opened along the newly built Baltimore National Pike, north from the Frederick Turnpike.

Catonsville was briefly made famous during the 1968 protest by the "Catonsville Nine", during which draft records were burned by Catholic anti-war activists.

In 2002, the Maryland legislature issued a proclamation declaring Catonsville to be "Music City, Maryland", because of the concentration of musical retail stores, venues and educational facilities in the area. Life Sounds Great is a series of compilation albums highlighting Catonsville musicians.

In 2007, Money magazine ranked Catonsville the 49th best place to live in the United States and the third best in Maryland and Virginia.

Catonsville is located at 39°16′26″N 76°44′17″W / 39.27389°N 76.73806°W / 39.27389; -76.73806 (39.273756, −76.738012). According to the United States Census Bureau, the CDP has a total area of 14.0 square miles (36 km2), all land.

Catonsville lies above the Fall Line within the Piedmont Region of Maryland, a region characterized by broad, rolling hills punctuated by streams and rivers. Catonsville overlooks the coastal plain and Chesapeake Bay to the East. The Appalachian Mountains lie approximately 40 miles west of the town.

Catonsville is centered along Frederick Road (Maryland Route 144), once the main road from Baltimore leading to points west replacing what is now called Old Frederick Road. Johnnycake Road and Academy Road form the northern and northeastern boundaries of Catonsville, the Patapsco River provides the western and southern boundaries, Gun Road, Shelbourne Road Linden Avenue, Circle Drive and Wilkens Avenue form the southeastern boundaries while Baltimore City forms the eastern boundary. Catonsville is bordered by Woodlawn to the north, Baltimore to the east, by Arbutus to the southeast, by Ilchester to the southwest, and by Ellicott City to the west.

In addition to Frederick Road (Exit 13), Interstate 695 (the Baltimore Beltway) services Wilkens Avenue (Maryland Route 372), Edmondson Avenue and the Baltimore National Pike (U.S. Route 40) via Exits 12, 14 and 15, respectively, with the latter two thoroughfares later converging in Baltimore City to the east. The main north–south roads in the area are Rolling Road (which is also Maryland Route 166 south of Frederick Road), Ingleside Avenue and Bloomsbury Avenue.

Catonsville is a terminus of the Trolley Line Number 9 Trail and the Short Line Railroad Trail.

The Maryland Transit Administration provides bus service to the Catonsville area via the Purple CityLink route with service to Downtown Baltimore, LocalLink routes 37 and 77, and Express BusLink 150 to Columbia. MARC Train provides commuter train service at the nearby Halethorpe station in Arbutus.

Major north–south routes in Catonsville include:

Major east–west routes in Catonsville include:

In 2010 Catonsville had a population of 41,567. The ethnic and racial composition of the population was 73.4% non-Hispanic white, 14.3% non-Hispanic black, 0.3% Native American, 6.3% Asian, 0.1% Pacific Islander, 0.2% non-Hispanic from some other race, 2.4% from two or more races and 3.4% Hispanic or Latino from any race.

As of the census of 2000, there were 39,820 people, 15,503 households, and 9,255 families residing in the CDP. The population density was 2,843.9 inhabitants per square mile (1,098.0/km2). There were 16,054 housing units at an average density of 1,146.6 per square mile (442.7/km2). The racial makeup of the CDP was 82.28% White, 11.83% African American, 0.22% Native American, 3.61% Asian, 0.04% Pacific Islander, 0.59% from other races, and 1.43% from two or more races. Hispanic or Latino of any race were 1.87% of the population.

There were 15,503 households, out of which 25.7% had children under the age of 18 living with them, 46.7% were married couples living together, 9.9% had a female householder with no husband present, and 40.3% were non-families. 33.8% of all households were made up of individuals, and 17.4% had someone living alone who was 65 years of age or older. The average household size was 2.30 and the average family size was 2.98.

In the CDP, the population was spread out, with 19.9% under the age of 18, 12.0% from 18 to 24, 27.2% from 25 to 44, 20.7% from 45 to 64, and 20.2% who were 65 years of age or older. The median age was 39 years. For every 100 females, there were 86.0 males. For every 100 females age 18 and over, there were 81.9 males.

The median income for a household in the CDP was $53,061, and the median income for a family was $67,005. Males had a median income of $44,705 versus $33,420 for females. The per capita income for the CDP was $25,254. About 2.8% of families and 4.6% of the population were below the poverty line, including 3.3% of those under age 18 and 4.1% of those age 65 or over. The median house value for the CDP was $141,300 in the 2000.