Glenn Mortimer is not seeking re-election to the Mountainside borough council and will be replaced on the Republican organization line by Donna Pacifico.
Mortimer has served as a councilman since 1998, when he defeated Democrat Michael Krasner by 326 votes. He has been the Union County Republican chairman since 2014.
Mayor Paul Mirabelli and councilman René Dierkes have party support in their bid for re-election.
Democrats have not yet announced their candidates for mayor and council.
Republicans narrowly won a hotly contested race for council in 2018, with Democrat Ileana Montes, a former director of the state Division on Women, coming within 77 votes of incumbent Robert Messler.
Mountainside (pop. 6,685) is one of the last GOP strongholds in Union County. Donald Trump carried it with 56% and Leonard Lance with 63% in 2016. That’s not far off from where the borough was a decade ago, when Lance won 64% and John McCain received 61%. It’s been Republican almost forever: the GOP won borough council seats despite national Democratic wave elections, 1964 and 1974.