There are 67 counties in the state of Pennsylvania, located in the Northeastern United States of America. Lackawanna County became the 67th Pennsylvanian county in 1878.
Prior to Lackawanna County's establishment, Cameron County was the newest Pennsylvanian county, established in 1860. The first three counties in Pennsylvania, Bucks, Chester and Philadelphia counties, were established simultaneously in 1682. Counties in Pennsylvania are categorized into different classes based on their population, ranking from first class to eighth class. Pennsylvania's most populous county is Philadelphia County, a first-class county, which is home to the state's largest city, Philadelphia. Pennsylvania's least populous county is Cameron County, an eighth-class county.