The conference comprises 21 small public high schools with enrollments between 60-340 students in Carroll, Jo Daviess, Lee, Ogle, Stephenson, Whiteside, and Winnebago counties.

Initially three divisions were formed for all team sports except football: West - Dakota, East Dubuque, Galena, Lena-Winslow, Orangeville, River Ridge, Stockton, and Warren East - Ashton-Franklin Center, Durand, Kirkland-Hiawatha, North Boone, Pecatonica, Rockford Lutheran and South Beloit, and South - Forreston, Freeport Aquin, Fulton Unity Christian, Eastland, Pearl City, Milledgeville, Mt.

In 2000, after six schools (Ashton-Franklin Center, Durand, Kirkland-Hiawatha, North Boone, Pecatonica and South Beloit) left to form the Four Rivers Conference, the two remaining schools from the East, Rockford Christian Life and Rockford Lutheran, also left the conference looking for competition within closer proximity.

The Sobos joined the Northeastern Athletic Conference to compete against schools from Chicago, Rockford, Aurora, Arlington Heights, Elgin, Hebron, Crystal Lake, Ottawa, Mooseheart and Kirkland.

[1] To replace the exiting team, the NUIC added Amboy High School, formerly a member of the Three Rivers Conference.

These divisions remained constant with the only change occurring in 2016 when Amboy was added to the East to replace South Beloit after their departure.

Prior to the 2023-24 season, Orangeville and Aquin boys basketball began a coop, reducing the number of teams in the North to 6.

In the North, the Orangeville/Aquin coop was eliminated and Forreston was moved from the South to put the total number of teams at 7.

Durand, Pecatonica and South Beloit joined the Northwest Division and Ashton-Franklin Center entered the Upstate.

[13] This change, along with Warren forming a coop with Black Hawk High School in South Wayne, Wisconsin, has created a conference realignment specifically for football.

The 2022 season included: On November 18, 2021, the East Dubuque board of education voted 5 to 1 in favor of joining Southwestern High School (Wisconsin) for football, leaving the NUIC and bringing the total number of teams competing in 11-man football down to nine.

The 2024 season included the following alignment: In 2001, the conference utilized the same concept of North and South divisions for girls volleyball.

[18][19][20][21] [22][23][24][25][26][27][28][29][30][31] The conference also has produced 146 individual championships, including golf,[22] public speaking,[32] track & field,[23][29] and wrestling.

[33] Josh Alber and Seth Milks from Dakota are the only individual 4-time state champions in the history of the conference.

As a wrestler, Alber finished his 4 years of competition undefeated with a final record of 182 wins and 0 losses.

Alber also became the first four-time state champion in IHSA history to complete high school competition without a loss or tie.