St. Marys is a city in Elk County, Pennsylvania, United States. The population is 12,429 as of 2019. Originally a small town inhabited by mostly Bavarian Roman Catholics, it was founded December 8, 1842. It is home to Straub Brewery and the first Benedictine convent in the United States. In 1992, the borough of St. Marys absorbed the surrounding township of Benzinger and incorporated as a city. Despite its place as the second-largest city by area in Pennsylvania behind Philadelphia, its low population leads to it being one of the state's least dense cities.