Marienville is an unincorporated community and census-designated place in Jenks Township, Forest County, Pennsylvania, United States. Its altitude is 1,735 feet, and it is located at 41°28′12″N 79°7′29″W / 41.47000°N 79.12472°W / 41.47000; -79.12472. Other names for the community have included "Marion", "Marion Centre", and "Marionville". Marienville is a major point on a well-known ATV trail. According to the 2010 census the population of Marienville was 3,137.Marienville is the location of the SCI Forest state penitentiary.The community is in southeastern Forest County near the center of Jenks Township. Pennsylvania Route 66 is the main street, leading northeast 24 miles to U.S. Route 6 at Kane and southwest 27 miles to Interstate 80 near Clarion. Pennsylvania Route 899 leads south from Marienville 10 miles to Clarington.According to the U.S. Census Bureau, the Marienville CDP has a total area of 6.1 square miles, all land.