If we're talking about reforming state lines, North and South Dakota should really be merged; the only reason the Dakota Territory wasn't admitted as a single state was because the Republicans at the time wanted two extra Senators and the extra EV's.
Agreed. There is also a good argument for merging Idaho and Montana and having a single state of New England if we are going down this route...
Single state of New England might be too aggressive, but definitely merging Vermont, New Hampshire and Maine; and Rhode Island with either Connecticut or Massachusetts; would be reasonable.
Start with this map, and define the specified number of states in each region, that have between 0.5 and 1.5 of the ideal population. Existing state lines need not be followed.
Northeast (7 states):
North New England: ME, NH, VT 0.531 of ideal (capital Dixville Notch)
Massachusetts 1.061
South New England: CT, RI 0.750 (capital New London or Norwich) Connecticut qualifies to remain separate, so portions of RI could join Massachusetts.
New Jersey 1.424 so could remain whole.
Long and Staten Islands (capital Brooklyn)
Hudson Valley (capital Armonk) Manhattan, Bronx, Westchester, Rockland
Upstate New York (capital Syracuse)
Areas along the west bank of the Hudson might want to join the Hudson Valley, as well as counties further upstream.
Pennsylvania (2 states)
Philadephia is in East Pennsylvania and Pittsburgh in West Pennsylvania.
Ohio-Indiana (3 states)
Indiana can remain a State, so Cincinnati in South Ohio and Cleveland in North Ohio. Columbus would be like Brussels with a boundary along the 50 yard line at Buckeye Stadium, and the tuba player alternating between the two States.
Michigan-Wisconsin-Minnesota-Iowa (4 states)
Michigan is too large (1.603), and Iowa (0.494) too small to retain the existing states. I don't know whether Northlands (just north of Saginaw to Fargo) including Appleton, Oshkosh, Green Bay, Superior, and Duluth has enough population (3.1 million). This would permit a merger of the remainder of Minnesota with Iowa.
Alternatively, UP Michigan gets added to Wisconsin, and Iowa persuades some Minnesotans to become Iowans.
Illinois (2 states)
Chicagoland (7 counties, 1.35 of ideal, capital West Chicago)
Illinois (0.65, capital Springfield)
Missouri (1 state) 0.971 of ideal.
North Carolina-Virginia-Maryland-Delaware (4 states).
North Carolina is over 1.5 times the ideal, while Maryland-Delaware is just over (1.082). So there would be 3 states formed from Virginia and North Carolina.
One possible split would be three strips: Tidewater, Piedmont, and Mountains, but it might be difficult to get enough people in Mountains without going a lot further east than Roanoke, Asheville, and the Shenandoah.
So maybe Tidewater (extending south from the Chesapeake Bay to Wilmington, and then Central Virginia, and West North Carolina.
Kentucky-West Virginia (1 state)
Kentucky (0.704) has enough population to remain independent, so West Virginia could go elsewhere.
Tennessee (1.031) remains independent.
Georgia-South Carolina-Alabama (3 states)
South Carolina (0.751) and Alabama (0.777) have enough to remain independent, but Georgia 1.573 has too many. So perhaps Savannah and Augusta to South Carolina, and Columbus to Alabama.
Florida (3 states)
North Florida, including Jacksonville and Orlando.
Gulf Florida, including Tampa, St.Petersburg, and Sarasota
Gold Coast, including Miami, Fort Lauderdale, and (West) Palm Beach.
Mississippi-Arkansas (1 state)
Arkansas (0.473) and Mississippi (0.482) are too small to remain independent. Capital, Greenville.
Texas-Louisiana-Oklahoma-Kansas (6 states).
Louisiana (0.736) is large enough to remain independent, but Kansas (0.436) is not. Oklahoma+Kansas is about the right size (1.072) for a state, capital in Tulsa, Wichita, Guthrie, or Baxter Springs.
Divide Texas into 4 states:
South Texas (capital Houston)
North Texas (capital Fort Worth or Plano)
Central Texas (capital San Antonio, New Braunfels, San Marcos, Temple, or Waco)
Rio Grande (capital Del Rio)
Nebraska-South Dakota-North Dakota-Wyoming-Idaho-Montana (1 state)
Capital of Upper Louisiana is Rapid City, Sturgis, or Deadwood.
Arizona (1.037) remains independent.
Colorado-New Mexico-Utah-Nevada (2 states)
Utah-Nevada (0.836) becomes state of Deseret, with capital alternating between Provo and Las Vegas.
Colorado-New Mexico (1.150) becomes Colorado.
Washington-Oregon-Hawaii-Alaska (two states)
Washington (1.092) can remain independent.
Oregon-Hawaii-Alaska form the other state (0.960)
California (6 states)
Northern California
Bay Area
Central California
Los Angeles
Coastal Southern California
Desert Southern California