Saint Agatha was settled by French Acadians, its name derived from the parish church that was established in 1890, itself named for a Sicilian saint of the 3rd Century who was martyred for her Christian beliefs. The town incorporated on March 17, 1899 from a portion of Frenchville; and in 1927, it annexed additional land from Frenchville.
Saint Agatha is located on the northwestern shore of Long Lake, and accessed from Maine Route 162 from Frenchville, which hugs the shore and continues along nearby Mud Lake.