| St. Mary's High School | |
| Streetaddress: | 142 Laverack Avenue |
| City: | Lancaster |
| State: | New York |
| Zipcode: | 14086 |
| Country: | United States |
| Religion: | Roman Catholic |
| Head Of School: | Kevin Kelleher |
| Chaplain: | Robb Ciezki (Deacon) |
| Teaching Staff: | 28[1] |
| Ratio: | 11:1 |
| Type: | Private, Coeducational |
| Grades: | 9-12 |
| Conference: | Monsignor Martin Athletic Association |
| Motto: | Bonitatem et disciplinam et scientiam doce me. |
| Motto Translation: | Teach me goodness kindness and discipline. |
| Rival: | Lancaster High School (New York), Depew High School, Cardinal O'Hara High School (Tonawanda, New York) |
| Patron: | The Blessed Mother under the title of Immaculate Heart of Mary |
| Nickname: | Lancers |
| Yearbook: | The Lance |
| Publication: | Legends (literary magazine), The Lance (alumni paper) |
| Newspaper: | The Marian Gazette (monthly newsletter, formerly "Currents")[2] |
| Established: | 1904 |
| Enrollment: | 411[3] |
| Enrollment As Of: | 2020-21 |
St. Mary's High School is a co-educational, Roman Catholic high school located in Lancaster, New York, 4.5 miles South East of the Buffalo Niagara International Airport and 14.5 East of downtown Buffalo. The school is within the Diocese of Buffalo. St. Mary's enrollment includes students in grades 9-12 from four counties and approximately 30 school districts. The current "Head of School" is Kevin Kelleher.