A Holliston landmark, St. Mary's Catholic Church also houses one of the largest congregations in town, with over 2,200 families. A member of the Archdiocese of Boston, St. Mary's was founded in 1870 and now hosts a number of religious education programs, youth and liturgical ministry programs, a music program and adult faith groups in addition to several social outreach initiatives.

St. Mary's holds mass six days a week (Mon - Sat, 9am) in addition to Saturday and Sunday vigils (Sat, 5 and 7:30pm; Sun, 7:30am, 9:30am and 11:30am) and on holy days (as announced). The church also performs adorations (first Fridays, 9:30am - 10:30 am), confession (Sat, noon - 12:45 pm or any time by appointment), anointing of the sick (b y appointment), baptisms (the second and fourth Sunday of each month) and marriages (call six months in advance).