While the ICA loves mountain biking too, the permitting and governance of mountain bike races falls on the USAC regional coordinator, not the Illinois Cycling Association.
A few good Illinois resources for mountain bike racing (and where to go mountain biking in general) are the Chicago Area Mountain Bikers, Peoria Area Mountain Bikers Association, and The Bonebell.
2021 Illinois MTB State Champions
14U Cat 3 Junior Women
Hannah Moeching
14U Cat 3 Junior Men
Jacob Anderton
Cat 3 Novice Women
Alexa Perrow
19-29 Cat 3 Novice Men
Mateo Beeney
30-39 Cat 3 Novice Men
Mike Herr
40-49 Cat 3 Novice Men
Daniel Johnson
50-59 Cat 3 Novice Men
Daniel Kolar
19-29 Cat 2 Sport Men
Kevin Ramos
30-39 Cat 2 Sport Men
David Hakes
40-49 Cat 2 Sport Men
Justin Stevens
50-59 Cat 2 Sport Men
Michael Carney
60+ Cat 2 Sport Men
Jerry Porter
39 & Under Cat 1 Expert Women
Brianna Overby
40+ Cat 1 Expert Women
Beverly Enslow
40-49 Cat 1 Expert Men
Michael Robertson
50-59 Cat 1 Expert Men
Jarrod Kerkhoff