St. Johnsbury Academy (SJA) is an independent, private, coeducational, non-profit boarding and day school located in St. Johnsbury, Vermont, in the United States. The academy enrolls students in grades 9-12. It was founded by Thaddeus Fairbanks, and accepts the majority of its students through one of the nation's oldest voucher systems. It has a sister school, St. Johnsbury Academy Jeju in Jeju Island, South Korea.

St. Johnsbury is the shire town of Caledonia County, Vermont, United States. As of the 2020 census, the population was 7,364. St. Johnsbury is situated on the Passumpsic River and is located approximately six miles northwest of the Connecticut River and 48 miles (77 km) south of the Canada–U.S. border.