The Illinois Thunder were an indoor soccer club (based in Rockford, Illinois) that competed in the National Professional Soccer League.
After the 1991/92 season, the team became the Denver Thunder.
| Year | Division | League | Reg. season | Playoffs | Avg. attendance | |
|---|---|---|---|---|---|---|
| 1990–91 | 2 | NPSL | 4th, National | Did not qualify | 1,613 | |
| 1991–92 | 2 | NPSL | 3rd, National | Quarterfinals | 2,160 |