St. Marys is a city located in Pennsylvania. With a 2020 population of 12,100, it is the 53rd largest city in Pennsylvania and the 2708th largest city in the United States . St. Marys is currently declining at a rate of -0.66% annually and its population has decreased by -7.42% since the most recent census, which recorded a population of 13,070 in 2010. St. Marys reached it's highest population of 14,502 in 2000. Spanning over 100 miles, St. Marys has a population density of 122 people per square mile.
The average household income in St. Marys is $70,662 with a poverty rate of 8.03%. The median rental costs in recent years comes to $584 per month, and the median house value is $122,600. The median age in St. Marys is 47.6 years, 46.1 years for males, and 48.9 years for females.