First-term Ward 4 Alderwoman Kathleen Sader resigned from the Olean Common Council on Wednesday.
She said her resignation is effective immediately because she intends to move out of the city with her husband and children to the Village of Allegany.
She said the chain of events leading up to her announcement was a fluke.
Sader is a Republican who in 1999 won the seat held by her father-in-law, Robert Sader, from 1994 to 1999.
Robert Sader did not seek his party's nomination that year. Sader said her father-in-law is now anxious to regain his seat. He has received the Republican Party endorsement in Ward 4 and will face Democratic candidate John Ballak.
The vacancy could be filled temporarily by appointment.
"I have a small piece of advice for anyone even remotely thinking of serving in local city government -- just do it," Sader said, noting she intends to continue working as a volunteer with the city Republican Committee as long as she can.
Sader was a Democrat when she received the Republican Party's endorsement to run against fellow Democrat Barry Gan. She changed her party affiliation to Republican after her 1999 election victory.