Carroll County was created in 1837 from parts of Baltimore and Frederick Counties.
During the American Civil War, the population of Carroll County was sharply divided between supporters of the Union and the Confederacy. In 1863, there were significant troop movements through the county as part of the Gettysburg campaign. On June 29, 1863, the cavalry skirmish known as Corbit's Charge was fought in the streets of Westminster, when two companies of Delaware cavalry attacked a much larger Confederate force under General J.E.B. Stuart.
Notable citizens of Carroll County include:
Francis Scott Key, author of the Star Spangled Banner, was born at his family plantation of Terra Rubra, in what is now western Carroll County.