Savages.
Whiterun Citizens. Or Whiterunners, if you HAVE to have a one-word answer.
They're Nords but since that has already been shot down try something tied into the name of the keep.........
People don't seem to understand the names/nicknames people from different cities get. Maybe it isn't an American thing.
In England, Geordie = from Newcastle. Scouser = from Liverpool. Cockney = from London. Tyke = from Leeds.
That's what the OP is getting at.
Anyways, Whiterunners is probably the closest to realistic, or planesmen.
It's Chicagoans (I used to be one), Charlestonians and Romans. There are also Los Angelinos, Parisians, Muscovites, Mancunians, Athenians, Glaswegians, and dozens of other names for the citizens of various cities.
My vote is for Whiterunian.
Citizens of Whiterun. I do NOT think of Whiterunners, Falkreathians, Markarthians, Ivarsteadians, Solitudians, etc, etc.
Nord is a term more comparable to European or Caucasian.
'People of Whiterun', just as Marammal preaches to the 'people of Riften'.
Really, the only city that has an awesome word for it's citizens is Solitude ...
I thought Romans referred to all citizens of Rome, not just the city.
As for Charlestonians I live in Charleston and have never heard that in my entire life, lol. Probably because of how silly these names are.
but the other guy said to call the people of the plains which sounds about right