St. John's Northwestern Military Academy (SJNMA) was founded in 1884 as St. John's Military Academy (SJMA) in Delafield, Wisconsin, by the Rev.

Sidney T. Smythe as a private, college preparatory[1] school.

SJNA (St. John's Northwestern Academies) is a coed independent boarding and day school for boys and girls in grades 6–12.

[2] St. John's Northwestern campus consists of a collection of historic buildings, many with towers and battlements in a style that suggests a Medieval castle, with most of them arranged in a U around the drill field.

In 1977 these historic campus buildings were listed on the National Register of Historic Places for the complementary design of many of them and since the school is the oldest military academy in Wisconsin.