I've lived in a lot of places in the U.S. and the county designation is used many different ways. Generally, in the eastern states, it's an administrative governmental thing, and in the west it's also a geographic thing. In Wyoming, auto license plates are numbered according to county, the numbers were set by county population at the time the whole thing was set up. For instance someone from Casper would have a plate that read 1-2345 for Natrona County, and someone from Cheyenne would have 2-2345 for Laramie County.
Once you learn the numbers you know from the plate where someone is "from." That's handy when you need a group to dislike, as in "them Damn Converse County jerks come here and catch our fish..." (Would this be called countyism?)
I reckon the use of "the" in Irish counties is a local custom that didn't travel well. In Amerikay you hear "The County Down" in the songs, but if you ask "Where you from?" the response is or was, generally just "County Cork," not "The County Cork."
I've never quite understood the Irish counties. Near as I can tell, there are 32 irish counties located within 4 Irish counties. Anyone know how this works?

O'Meara

Whoops, I meant The O'Meara.