[2] Demmer was born and raised in Dixon, Illinois, where he continues to live with his wife.
The Lee County Industrial Development Association is a not-for-profit organization whose mission is to promote, develop, and facilitate industrial, commercial, and business enterprises in Lee County[6] Demmer was a top Illinois House Republican[7] who served as Deputy Republican Leader from 2018 to 2023.
[8] Demmer was the chief budget negotiator for the Illinois House Republicans,[9] and was the caucus leader on Medicaid and healthcare policy issues.
[12] Demmer was the Republican Spokesperson[13] on the Special Investigating Committee II in 2020 to investigate the conduct of Michael Madigan, the then-Speaker of the Illinois House of Representatives, who was later indicted by a federal grand jury on 22 counts of racketeering and bribery in connection with alleged corruption schemes.
[14] Demmer served as an Illinois co-chair for the John Kasich's 2016 presidential campaign.