St. Marys is a city located in Pennsylvania. With a 2020 population of 12,187, it is the 52nd largest city in Pennsylvania and the 2685th largest city in the United States. St. Marys is currently declining at a rate of -0.70% annually and its population has decreased by -6.76% 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 123 people per square mile.
The average household income in St. Marys is $69,478 with a poverty rate of 7.70%. The median rental costs in recent years comes to $601 per month, and the median house value is $116,400. The median age in St. Marys is 46.8 years, 44.9 years for males, and 49 years for females. For every 100 females there are 99.4 males.