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. Other names for the community have included "Marion" 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.