Thomas Connelly, 34, agreed to the sentence when he entered his guilty plea Wednesday, according to the DuPage County state’s attorney’s office.
Connelly had inappropriate sexual relations with a female student in May 2017 at a Naperville hotel, prosecutors said. The girl was between 13 and 17 years old, according to the charges.
At the time, Connelly was a physics teacher at Joliet Central High School, prosecutors said. Authorities were tipped off about the sex assault when staff overheard students talking about a sexual relationship between a student and teacher, prosecutors said.
Connelly, of Chicago, was free on bail following his arrest in July 2019, but was taken back into custody Wednesday to begin serving his sentence.
Connelly is required to serve 85% of his sentence before he’s eligible for parole. He must register as a sex offender upon release.