Taking its name from the Township of Guysborough, which was named in honour of Sir Guy Carlton, Guysborough County was created when Sydney County (Antigonish County) was divided in 1836.
In 1840, the Township of St. Mary's, in Guysborough County, was set off as a separate and distinct District. In 1863 the dividing line between Halifax and Guysborough Counties was altered and a polling district was added to Guysborough County.