The Sioux Valley was formed in November 1933, holding its first championship competition later that season in the form of a basketball tournament. The conference was originally composed of six schools: Aurelia and Marcus of
Cherokee County, Alta and Sioux Rapids of
Buena Vista County, and Paullina and Sutherland of
O'Brien County. By 1942, the conference had expanded to 10 members. After the exit of Marcus for the 1936–37 school year, Hartley and Primghar joined the conference. The next year, Cleghorn joined. Sanborn became the ninth member in 1941, and Milford became the tenth for the 1942–43 school year. Due to
World War II, competition was put on hold for one year, though some schools continued to field athletic teams, in 1944–45. When play resumed the next season, Cleghorn opted not to return to the league. Four years later, Sioux Rapids, which was the smallest school in the league, dropped out to compete in a new league, the Little Northwestern Conference. Harris–Lake Park also competed in the conference for a brief period in the 1960s and 1970s as a football-only member. During this time Sanborn did not compete in the league for football. For the next 40 years, the conference lineup would continue unchanged. During this time the conference established itself as one of the premier small-school conferences in the state, especially in basketball, as the conference won 6 of the first 15 Class 1A basketball tournaments staged by the
Iowa High School Athletic Association. Conference schools were also traditionally strong in track & field, as a conference school placed in the top two at the state meet 15 times between 1956 and 1989. ==State qualifiers==