Tom Determann serves as an at-large council member and was elected to the Clinton County Board in the November election.
He has declined to reveal his intentions about resigning from the council.
County Attorney Mike Wolfe has issued an opinion that Determann could not serve on both bodies at the same time.
Clinton Mayor Mark Vulich, in an email to other council members, city staff and the media, released the short resignation note late Monday night.
Determann stated he was resigning his council seat effective December 31st, 2016.
The terms for Clinton County officials elected in November officially begin today.
The Clinton County Board has its first meeting of the year this morning.
By Dave Vickers, KROS, Clinton