The first European contact with the district occurred when Captain Tobias Furneaux sighted and named the 694 metre St Patrick's Head in 1773.
Settlement in the area began in the 1840s with the establishment of a convict probation station. Both St Mary’s Pass and Elephant Pass were carved out by a team of 300 convicts, connecting the area to the coast. The site of the station was called Grassy Bottom.

A "prime mover and shaker" for the construction of the Pass had been a Scot, James Grant of "Tullochgorum". While delighted that the construction was to proceed, the local "establishment" was less than pleased with the prospect of "Grassy Bottom Pass" appearing on the map. Grant wrote to the Surveyor General in June 1842, and proposed that the Pass be called "St. Marys Pass".

Prior to the 1840's the area was generally known as the St Patricks Head District,but then the property of "Cullenswood" developed as a de facto township,until in the 1860's St. Marys took over as the capital of the Break-O'Day Plains.

A now-vanished railway line reached the town in 1866, but the original railway station can still be seen in the town.

St Marys’ 150th anniversary was celebrated in 2007.

St Marys is close to many local attractions: you can try the challenging climb to the top of St Patricks Head, or the more accessible South Sister Peak, for stunning forest and coastal views, there are also spectacular views from Elephant Pass.

The Coalminers’ Heritage Wall and Heritage Walk at the tiny settlement of Cornwall is a monument to the miners who hand-tunneled a coal mine beneath the Mt. Nicholas Range.

You can also visit nearby waterfalls, go fishing at Lake Leake or bush walking in Douglas Apsley National Park.

St Marys It offers a range of accommodation, a craft gallery, bakery, shops and supermarkets, and the St Marys Hotel, built in 1916, which dominates the town centre.