The2021 Southern Illinois 100 presented by Lucas Oil was the 17thstock car race of the2021 ARCA Menards Series season, and the 35th iteration of theevent. The race was held on Sunday, September 5, inDu Quoin, Illinois at theDuQuoin State Fairgrounds Racetrack, a 1 mile (1.6 km) permanent clay oval-shaped track at theDuQuoin State Fair. The race took 104 laps to complete due to an overtime finish. At race's end,Landen Lewis ofRette Jones Racing would dominate the race, leading every lap en route to his first careerARCA Menards Series win.^[1] To fill out the podium,Ty Gibbs ofJoe Gibbs Racing andKen Schrader ofFast Track Racing would finish second and third respectively.

TheDuQuoin State Fair was founded in 1923 by local businessman William R. "W.R." Hayes, who owned the fair and ran it. (It did not become run by the state of Illinois as a true "state fair" until the 1980s; it is now officially called the Illinois State Fair in DuQuoin, as opposed to the longtime one at state capital Springfield.) At the start Hayes had a half-mile harness-racing track on his 30-acre site, with wooden grandstands that seated 3000. In 1939 Hayes started buying adjoining stripmined land to develop its potential as parkland, replanting it and turning the strip pits into family-friendly ponds and lakes. He eventually expanded his little fairgrounds into 1200 acres.

The DuQuoin "Magic Mile" racetrack was constructed on reclaimed stripmine land in 1946 by W.R. Hayes. The track's firstnational championship race was held in September 1948. In the second race on October 10, popular AAA National driving championTed Horn was killed in the fourth turn when a spindle on his championship car broke. The national championship race for theUSAC Silver Crown dirt cars is held in his honor.

The only 45-minute practice session was held on Sunday, September 5, at 4:15 PMCST.^[2]Jesse Love ofVenturini Motorsports would set the fastest lap in the session, with a lap of 36.037 and an average speed of 99.897 miles per hour (160.769 km/h).

Qualifying would take place on Sunday, September 5, at 6:00 PMCST. Each driver would have one lap to set a time.^[2]Landen Lewis ofRette Jones Racing would win the pole for the race, setting a lap of 34.236 and an average speed of 105.152 miles per hour (169.226 km/h).^[3]

No drivers would fail to qualify.Jesse Love andKelly Kovski did not make a qualifying lap, and had to start the race from the rear.

• 2021 ARCA Menards Series
• September 2021 sports events in the United States
• 2021 in sports in Illinois
• NASCAR races at DuQuoin State Fairgrounds Racetrack

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