The latest defection came as a major shock to Sinn Féin, especially as the councillor concerned had just two weeks earlier sought a nomination to run for the party as a general election candidate in the Cork North Central constituency.
Glanmire-based councillor Ger Keohane, informed the council and Sinn Féin party headquarters of his decision yesterday.
The news comes after the party earlier lost Cobh councillor Kieran McCarthy and Mitchelstown councillor June Murphy to the Independent benches following an internal spat which angered Mr McCarthy so much he decided to run against the party in the Cork East constituency in the general election next year.
Sinn Féin has now dropped to seven seats on the council from the 10 it had.
The Independents have risen from 10 in June 2014 to 15 now, and are just behind Fianna Fáil and Fine Gael which have 16 each.
Mr Keohane was unavailable for comment last night, but SF’s party whip on the council, Donnchadh O’Laoighaire, said he had been informed of the move by his party’s headquarters.
“Nobody wants to lose a councillor,” said Mr O’Laoighaire. “Ger’s resignation came as a surprise particularly as he put his name forward for selection two weeks ago for general election nomination. I don’t know what his long-term plans are.
“Yes, it’s disappointing but we will continue to provide the strongest voice of opposition on Cork County Council.”
Declan Hurley, spokesman for the Independents on the council, said he had been aware for some time that Mr Keohane was not happy.
“He’s a community-based councillor who feels he can’t represent his constituents through Sinn Fein,” said Mr Hurley. “We’d be delighted to have him.”