 sullivan county is a county located in the u.s. state of pennsylvania. as of the 2010 census, the population was 6,428, making it the second-least populous county in pennsylvania. its county seat is laporte. the county was created on march 15, 1847, from part of lycoming county and named for charles c. sullivan, leader of the pennsylvania senate at that time. ==history== the land which became sullivan county was originally purchased from the iroquois by the province of pennsylvania in 1768, as part of the first treaty of fort stanwix. it was then part of northumberland county, then became part of lycoming county when it was formed in 1795. sullivan county itself was formed from the northeastern part of lycoming county on march 15, 1847. it was the thirteenth and last county formed at least partly from lycoming county (and the fifth
1847_establishments_in_the_United_States Counties_of_Appalachia Pennsylvania_counties Sullivan_County,_Pennsylvania