In the South East, they bring you sweetened (usually far too sweetened for my tastes) iced tea. This is amazingly universal.
I live in NC and have been probing the border for years.
For “nicer” restaurants, the universal sweet tea boundary seems to be precisely at the NC/VA border.
US Midwest - the restaurants I visit don’t have iced tea (IF they serve cold tea, it’s the premade kind at the soda fountain). I get a cup of hot water, a single bag of black tea, and sometimes a lemon slice. If there isn’t sugar at the table you have to ask for it.
Where the hell are you in the midwest that they don’t have iced tea? It’s ubiquitous in my experience.
Not a guarantee here in northern Indiana.