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.

The area of present-day Catonsville was not inhabited by large numbers of Native Americans, rather serving as a hunting ground or a means of transit. However, Native American arrowheads found in the area signal a presence in small numbers. The Patapsco River itself, forming the southern boundary, bears a Native American name. They would have disappeared long before the first settlers encroached on the area, however.

The Native Americans had left behind a number of trails, some of which the earliest settlers adopted them for their own purposes. Rolling Road, for example, originated as a Native American trail, beginning from Elkridge Landing, and traveling north through present-day Catonsville—the road was repurposed as a "rolling road" used to roll hogsheads of tobacco, hence its current name. Another trail was the Old Frederick Road, now known regionally as Johnnycake Road, which began at a point along Gwynns Falls, and traveling northwest, forming what is now Catonsville's northern boundary. Another potential Native American trail is Old Frederick Road, branching off from the aforementioned road southwest toward Frederick Road near Ellicott City.

The Catonsville region and the surrounding Patapsco River valley remained unsettled for much of Maryland's early history, as early communication depended on major bodies of water, and not by land. Before the first settlers arrived, the region of present-day Catonsville served as hunting grounds, and was known in the 17th century and early 18th century as Hunting Ridge. Early colonial hunters and trappers subsisted off game such as deer to feed and clothe themselves. However, it would be decades before the region underwent the settlement process.

The earliest settlement of present-day Catonsville began in the second half of the 17th century. Incoming settlers at first followed streams by boat or trail, until embarking further uphill for uncultivated land, often using the aforementioned Native trails, as existing settlers took up most of the desirable land around major waterways. It is uncertain if Catonsville's earliest settlers came primarily via the Patapsco or Patuxent rivers. Settlers from the latter would have traversed Anne Arundel County, before fording the Patapsco River at Elkridge Landing. As the southern shore of the Patapsco River began to fill with settlers, others began to look northward, a movement which soon increased in rapidity through the latter decades of the century. By the year 1695, much of Hunting Ridge had been settled through land grants, and most of present-day Catonsville land comes from these original land grants.

The history of present-day Catonsville follows its main artery, Frederick Road, which the town eventually developed around. 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.