Catonsville is a census-designated place (CDP) in Baltimore County, Maryland, United States. The population was 39,820 at the 2000 census. Catonsville is bordered by Woodlawn to the north, by Baltimore to the east, by Elkridge to the south, and by Ellicott City to its west. Catonsville is the home of University of Maryland, Baltimore County (UMBC), a public research university with over 12,000 students.