The first settlers arrived at the junction of the Thames River and Trout Creek, southwest of Stratford in the early 1840s, attracted by the area's natural resources. At the new town site, the Thames River cascaded over a series of limestone ledges, providing the power to run the first pioneer mills and giving the community an early nickname: Little Falls.
The arrival of the Grand Trunk Railway in the late 1850s increased the growth; the community became a centre for milling, grain-trading and the manufacture of agriculture-related products.
In the riverbed and along the banks, limestone was close to the surface and could be quarried for building materials. Many 19th-century limestone structures survive: churches, commercial blocks, and private homes. They have given St. Marys its nickname: Stonetown.
St. Marys is near Highway 7 southwest of Stratford. If coming from the east (Stratford and beyond), turn right on Perth Road 9. If coming from the west, turn left on either Perth Road 123 or Perth Road 120A.
VIA Rail's Toronto-to-Sarnia train stops in St. Marys.
- Limestone buildings. St. Marys contains many 19th-century buildings built with locally quarried limestone. Notable buildings include the Opera House built in 1880, the spired municipal Town Hall built in 1891, and the Public Library built in 1904. The Municipal Heritage Committee helps in preserving the historic stone buildings and publishes a useful brochure online, with interesting facts about those in the downtown area.
- Canadian Baseball Hall of Fame, 386 Church St. S., ☏ . May-Aug: Tu-Su and holiday Mondays 10AM-5PM. The Hall of Fame moved to St. Marys from Toronto in 1994 and opened in 1998. It is dedicated to preserving Canada's baseball heritage. Since opening, 75 members (46 players, 23 builders, 2 honorary, 4 honorary teams) have been inducted. It includes professional ballplayers, amateurs, builders, and honorary members who have helped popularize the sport in Canada. The facility also includes a baseball field designed by landscape architect Art Lierman of London, Ontario. There are thousands of artifacts on display in the museum "including Fergie Jenkins and Larry Walker memorabilia, artifacts from Canada's two major league franchises, the Toronto Blue Jays and the Montreal Expos, a Babe Ruth collection, a large display on all the current MLB Canadians and a tribute to the Canadian women who played in the All-American Girls Professional Baseball League." Adult/senior $12, children (ages 10-17) $10, children (ages 9 and under) free, family (2 adults/4 children) $35.
- St. Marys Junction Railway Station. This stone station is the only original Grand Trunk station in Southwestern Ontario. Although a National Historic Site, the station had been fenced off and neglected for a long time but is now slowly being restored.
- St. Marys Museum, 177 Church St. S., ☏ . This museum illustrates the history of St. Marys.
- Grand Trunk Trail. A 3.2-km-long paved trail, converted from an abandoned railway. The railway bridge over the Thames River is beautiful. The trail leads to the St. Marys Junction Railway Station. In 2012, the Re-Purposing of the Sarnia Bridge to part of the Grand Trunk Trail was inducted to the North America Railway Hall of Fame.
- Riverview Walkway. A paved trail that runs alongside the river. Beautiful views of the river on the one side and industrial remnants of the other.
- 1 St. Mary's Quarry, Water St. S.. The Quarries consist of two former limestone quarries located in southern St. Marys, one of which has been rehabilitated as an outdoor swimming pool. The area became a popular swimming spot with locals after filling with water between 1930 and 1935. In 1945 the town bought the quarries along with 50 acres (200,000 m²) of surrounding land, and now manages it as a public recreational facility. The quarry is Canada's largest outdoor swimming pool.
- The Town Hall Theatre. offers theatrical productions and events.
- Pass It On Store, 31 Water Street, ☏ . M–F 10AM-5PM, Sa (and Su in summer) 10AM-4PM. Vintage and antique store.
- Jennies, 83 Queen Street, ☏ . M-F 7AM-2PM, Sa 8AM-2PM. Breakfast and lunch. Sandwiches from $6, lunches $10-12..
- Harris Electric Eatery, 159 Queen St E, ☏ . Tu-Sa 11:30AM–2PM and 4:45–8:45PM. French, Mexican, burgers... maybe they should call it an "eclectic eatery".
- Sunset Diner, 343 Queen St W, ☏ . M Tu Sa 6AM-8PM, W-F 6AM-9PM, Su 7AM-8PM. Burgers, sandwiches, wraps, fish and chips, liver and onions, since the 1950s.
- 1 Parkview Creamery Bar and Grill (formerly O'Leary's Pub), 120 Parkview Drive, ☏ . Pub in beautiful old building with a view to the water.
- Stone Willow Inn, 940 Queen St. E, ☏ , toll-free: . Check-in: 3PM, check-out: 11AM. Spacious rooms, free wireless Internet and luxurious "Willow wonderful" bedding. Group rates; golf packages. Room with 2 double beds from $160.
- Westover Inn, 300 Thomas Street, ☏ . Pool, free parking, restaurant, WiFi, bar, golf course. From $150.