The Stone Town
Although St. Marys is politically independent of Perth County, it is enclosed by the Township of Perth South.
It is situated at the junction of Thames River and Trout Creek, southwest of Stratford.
The town is familiar with its nickname, "The Stone Town", due to the abundance of limestone in the adjoining area, giving rise to a large number of limestone buildings and homes throughout the town.
St. Marys contains many 19th century buildings some of them are the Opera House built in 1880, the spired municipal Town Hall built in 1891, and the Public Library built in 1904.
The Grand Trunk Trail, a transformed section of the former Grand Trunk Railway line, features a walk over the restored Sarnia Bridge, providing panoramic views over the town.