The DuPage County Coroner's Office identified the man as Ivan A. Perez, 33, of Pasadena, Texas.
His probable cause of death is accidental drowning.
Two contract workers went missing after being taken away by Monday's intense storms.
Both workers were employed by Vortex Lining Systems, a contractor hired by the village of Downers Grove for a storm sewer pipe rehabilitation project beneath downtown.
They were both working in the pipe in the 800-block of Curtiss Street when rising water swept them into the underground system. The storms were strong and caused heavy damage in DuPage County, flooding yards and splintering trees, even splitting some in half.
A Vortex employee flagged Downers Grove police officers down just before 1 p.m. Monday and told them that the contractors had become trapped in the pipe.
A woman who lives nearby said her neighbor heard someone screaming from the sewer on Monday.
Downers Grove firefighters rescued one contractor about 200 feet from the point where the crew entered the sewer around 3:15 p.m. Monday. He was taken to Good Samaritan Hospital in good condition.
But conditions became too dangerous for rescuers to continue on Monday evening, and the initial rescue mission became a recovery mission around 8:30 p.m. Monday. Recovery efforts continued overnight.
For most of Tuesday, crews were staged about a half-mile away in the area of Gilbert to Curtiss. But police, fire, and other emergency cruiser relocated to Washington and Curtis, staging around a blue tent.
Chopper 7 was over the scene when a man put on a harness, a helmet with a light on it, and other gear, possibly preparing to make a recovery effort.
Downers Grove fire officials said the missing contractor was found dead in the storm sewer near Washington Street around 5 p.m. Tuesday.