St. Marys is a city in Elk County, Pennsylvania, United States. The population is 12,738 as of the 2020 census. 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.