Former state Rep. Keith Farnham had a perfect attendance record at lawmakers' Springfield sessions this year until Wednesday, the day he resigned his seat citing "serious health issues."
Days before, U.S. Immigration and Customs Enforcement's Homeland Security Investigations searched Farnham's Elgin office and home, though authorities have not yet said what they were looking for.
A Daily Herald review of attendance records showed Farnham answered "present" to the Illinois House roll call each of the 12 times it met in 2014 before Wednesday.
Farnham resigned in a one-sentence letter to House Speaker Michael Madigan Wednesday, giving no explanation why.
In a statement released later, he said, "I have been battling serious health issues for a number of years and the coming months will require my full attention."
Farnham hasn't commented publicly otherwise.
House Speaker Michael Madigan said Thursday he knew nothing about what federal officials are looking for.
"No, no," Madigan told reporters. "You know what I know."
Farnham also plans to withdraw from the November ballot. Local party leaders could appoint someone to both run and serve the remainder of his term. No Republican has filed to run in the race, but the GOP could appoint a candidate, too.