Mark Mihal, 43, said he fell through the ground on the 14th hole at the Annbriar Golf Course in Waterloo while playing a round Friday, The (St. Louis, Mo.) Post-Dispatch reported Tuesday.
"I was standing in the middle of the fairway," Mihal said Monday. "Then, all of a sudden, before I knew it, I was underground."
Mihal was rescued by golfing companion Ed Magaletta and general manager Russ Nobbe, who brought a rope and a ladder.
Philip Moss, a geologist who examined the sinkhole, said it was the first confirmed case of someone falling into a sinkhole in Illinois.
"This guy just really was in the wrong place at the wrong time," Moss said.
Moss said sinkholes are common in the St. Louis area because the Limestone bedrock can dissolve in rainwater.
"It's a gradual process that creates a void in the soil," Moss said. "Over time, [the void] migrates upward through the soil to where the soil arch gets too thin to support the weight of what's over it, and it collapses."