From JMG’s Retrotopia; the flag of the Lakeland Republic, as he sees it. A nice, clean flag, able to be made at home, and with simple lines!
The exact colors weren’t specified, but perhaps in the Lakeland Republic, people don’t worry too much about these things.
For the Free City of Chicago, the current City of Chicago flag might be used:
Other flags were theorized, but they aren’t canon.
Update: 2016-Aug-04, the Atlantic Republic flag, from JMG’s post: “…the Atlantic flag, navy-white-navy with a gold anchor in the middle and a gold star in the upper left…”, and “The Atlantic Republic flag has horizontal stripes … the navy blue is rather darker — a good deep navy blue — and the gold anchor extends into the blue stripes above and below. The Chicago flag is good. The Confederate flag in 2065, by the way, is the famous “Bonnie Blue Flag”
So, the original:
And updated; navy blue is RGB (0,0,128).
More from JMG, regarding flags:
The Confederate flag in 2065, by the way, is the famous “Bonnie Blue Flag” — a single white star at the center of a blue field — and the song “The Bonnie Blue Flag” is the official national anthem, though you’ll hear “Dixie” at least as often; it has the same role as, say, “America the Beautiful” does in the US today. Texas still has the same flag it has today.”
So, we’ve got:
The flags of the Republic of New England and the Maritimes, the Missouri Republic, and elsewhere are not defined. In a previous post, I thought about some of these other flags. There is a flag of New England; the modern one with the six stars might be upgraded to include three stars for the Maritimes.