 According to the official state publication "Pennsylvania Local Government", Sullivan County was named for Pennsylvania state senator Charles C. Sullivan, who "took an active part in procuring passage of the bill" establishing the county.However, according to Frederic A. Godcharles (1933), the county is named for General John Sullivan, who led the Sullivan Expedition against the Iroquois in 1779.According to the U.S. Census Bureau, the county has a total area of , of which is land and (0.6%) is water.