The only plurality Irish ancestry counties in the US are in the Northeast (the furthest west is Lackawanna, PA and the furthest south is Cape May, NJ), except for interesting isolated exceptions in Butte-Silver Bow, MT and Loving, TX, which are both pretty demographically exceptional counties for a variety of reasons, but tend to be more suburban/exurban/rural rather than urban, not a huge surprise given that Irish-Americans mostly arrived a couple of generations before Italian-Americans.
I wouldn't characterize Butte as any of suburban/exurban/rural.
