The Loomis Chaffee School (/ˈluːmɪs ˈtʃeɪfi/; LC or Loomis) is an independent, coeducational, college preparatory school for boarding and day students in grades 9–12, including postgraduate students, located in Windsor, Connecticut, seven miles north of Hartford. Seventy percent of Loomis Chaffee's 726 students reside on the school's 300-acre campus and represent forty-four foreign countries and thirty-one U.S. states. 71% of Loomis Chaffee's student body are boarding students and 29% are day students.

Founded in 1914, Loomis Chaffee is a member of the Ten Schools Admission Organization.

The school was chartered in 1874 as The Loomis Institute by five Loomis siblings. The original 1640 Loomis Homestead was chosen as the site for the school, which opened in 1914. The forty-year gap between chartering and the opening of the school was due to the estate of the Loomis siblings being reserved for the siblings' retirement.

In 1910, John Mason Loomis's widow left over $1.1 million as an endowment to The Loomis Institute for charitable purposes. This donation allowed the school to remain tuition-free for its first four decades. In addition to being tuition-free, The Loomis Institute was distinguished from other New England preparatory schools by its lack of religious affiliation, offering of vocational education alongside college preparatory courses, and admission of both boys and girls.

The Loomis Institute ended coeducation in 1926 when The Chaffee School was incorporated to educate girls on an adjacent campus. In 1970, the boys and girls schools merged to form The Loomis Chaffee School. Since then, the school has expanded as its endowment, financial aid budget, faculty, and campus increased in size. Loomis had an acceptance rate of 7% for the 2023–2024 school year.

Loomis Chaffee competes in sports against schools from all over New England and adjacent states. The school is a member of the New England Preparatory School Athletic Council (NEPSAC) and competes in the Class A large school division. Additionally, Loomis is a member of The Founders League which comprises private schools located mainly in Connecticut.

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• (1914–1949): Nathaniel Horton Batchelder
• (1949–1952): William Speer
• (1952–1967): Francis Olmsted Grubbs
• (1967–1976): Frederick G. Torrey
• (1976–1996): John Ratté
• (1996–2008): Russell H. Weigel
• (2008–2024): Sheila Culbert
• (2024-Present): Jody Soja

Main article: List of Loomis Chaffee School faculty

Writer John Horne Burns taught at Loomis and wrote several books while there.

René Cheruy served for many years as head of the French department, as well as a member of the visual arts department.

• John Mason Loomis – American lumber tycoon and Union colonel during the American Civil War, and one of the Loomis family financiers and co-founders of the Loomis Institute
• James Chaffee Loomis – American lawyer, politician, and co-founder of the Loomis Institute
• Osbert Burr Loomis – American portrait painter and co-founder of the Loomis Institute

• Official website