Robert Linn has to be up there, he served as mayor of Beaver, Pennsylvania for 58 years from 1946 until his death in 2004 at the age of 95. What surprises me is that he was a Republican, I can't believe a Republican was elected in that area in 1946.
Just eyeballing it, it looks as though Republicans picked up the congressional district containing Beaver County in 1938 and held it through the 1940s. That area didn't become really Democratic until later: Mondale won Beaver County by more than Roosevelt did in any year except 1936 (and even that was close).
