St. Mary's is a census-designated place (CDP) located in and governed by Clear Creek County, Colorado, United States.

The CDP is a part of the Denver–Aurora–Lakewood, CO Metropolitan Statistical Area.

The population of the St. Mary's CDP was 333 at the United States Census 2020.

[1] The St. Mary's Glacier Metropolitan District and the St. Mary's Glacier Water & Sanitation District provide services.

The Idaho Springs post office (Zip Code 80452) serves the area.