For most of their athletics histories, the schools of the Missouri River Activities Conference were in other conferences. Beginning in the early 1970s, Sioux City schools began to compete with schools in
Sioux Falls, South Dakota, as a members of the boys-only Sioux Interstate Conference. In the late 1970s, the Sioux Delta Conference was formed between the Sioux City schools, LeMars Community, and Hull Western Christian to facilitate girls' athletic competition. A separate intrastate conference was necessary because the South Dakota High School Athletic Association conducted its girls' basketball tournament in the fall and volleyball tournament in the winter, opposite of many bordering states. From the 1920s to the 1950s C.B. Abraham Lincoln and Sioux City East competed with three Omaha high schools (
Central,
South and
Tech) and
Lincoln High in the Missouri Valley Conference.
Sioux City Central, which closed in 1975, was also a member. In spring 1997, the
South Dakota High School Activities Association effectively closed its borders to interstate athletic competition, forcing the dissolution of the Sioux Interstate Conference. The Sioux Delta Conference also dissolved that spring as both LeMars Community and
Hull Western Christian had by this time found homes in the
Lakes Conference, leaving the four Sioux City schools out in the cold. The Council Bluffs schools, meanwhile, were once part of the Omaha metro league which included numerous schools in Nebraska. After bowing out of the Omaha metro league, the two schools became charter members of the River Cities Conference, a league that included Nebraska schools such as Beatrice,
Ralston, South Sioux City,
Omaha Gross,
Omaha Roncalli, and
Omaha Skutt. With few options due to their size as 4A football schools, the Sioux City schools and Heelan sought out and were denied membership in both the
Central Iowa Metro League and the River Cities Conference. Undaunted, the schools petitioned the Iowa Department of Education for placement in an athletic conference. As a result of those proceedings, the Missouri River Conference was formed to meet the needs of the Sioux City schools, pulling the Council Bluffs schools out of the River Cities Conference to complete the six-school lineup. In 2010, Sergeant Bluff-Luton, a founding member of the
War Eagle Conference in 1979, began competing as the league's seventh school. LeMars Community announced in February 2018 that it would be joining the conference as the eighth member for the 2019–2020 academic year, leaving the
Lakes Conference. Hawkeye 10 Conference members
Lewis Central and Glenwood were also invited, but declined, opting to continue competing in the
Hawkeye Ten Conference. On June 20, 2025, the MRAC again offered
Lewis Central Community School District and
Glenwood Community School District to join as well as two other Hawkeye 10 Conference schools,
Harlan Community School District and
Denison-Schleswig. On August 19, 2025, Lewis Central accepted the invitation and will officially join for the 2026-2027 school year. At about the same time, Denison-Schleswig, Glenwood and Harlan each declined their invitations, opting to remain in the Hawkeye 10. ==Sports==