New York, Vermont, New Hampshire, Massachusetts, Connecticut, New Jersey, Florida, Pennsylvania, Ohio, Kentucky, Tennessee, Virginia, West Virginia, Maryland, Illinois, Delaware, Georgia, North Carolina, South Carolina, Alabama, Mississippi, Louisiana, and Texas. 24 states.
Mine are listed in this thread.
Split up by region because that makes me happy:
South: Alabama, Florida, Georgia, Louisiana, Mississippi, North Carolina, South Carolina, Texas, Virginia
West: Arizona, California, Colorado, Washington, Wyoming
Midwest: Illinois, Missouri
Northeast: New York, Pennsylvania
Plus DC, for a total of 19. I’m moving out of my parents’ house forever in a few days, so I should be able to add a lot to this list over the next few years.
Indiana, Nevada, New York and Illinois. And I know airports don’t count, but I’ve been to Philadelphia airport eight times and I’m only sixteen years old, so I think I’d like to add Pennsylvania to the list.
I actually live in the northwest of England, incidentally. 
I’ve never been to Rhode Island, Alaska, or Hawaii. All the rest, though.
Delaware
D.C.
Florida*
Georgia*
Maine*
Maryland*
Michigan*#
New Hampshire
New Jersey*
New York*#
North Carolina*#
Ohio
Pennsylvania*
South Carolina
Tennessee*
Vermont
Virginia*
West Virginia
Ontario*
Quebec
- – have spent the night in at last once
– have lived in
Virginia
Maryland
DC
Deleware
Pennsylvania
New Jersey
New York
Massachusetts
New Hampshire
Illinois
Michigan
Indianna
Ohio
Rhode Island
Florida
North Carolina
South Carolina
Georgia
Tennessee
Kentucky
Arizona
Califonia
Utah
New Mexico
West Virginia
Only 22 states myself.
I forgot about Wisconsin, so 22 states
I’ve been to 38 states plus DC (actually set foot in each one, not just drove through). The missing states are:
Alabama
Alaska
Arkansas
Hawaii
Idaho
Kentucky
Louisiana
Mississippi
Montana
North Dakota
Oregon
Washington
On the other hand, I’ve been to only one Canadian province (Ontario). The only foreign countries I’ve been to, besides Canada, are: Israel, the UK, and Poland.
Went from NYC to Seattle on the train, does that count?
20, 21 with D.C.
Arizona
Colorado
Florida
Georgia
Illinois
Indiana
Iowa
Kansas
Kentucky
Maryland
Michigan
Nebraska
New York
North Carolina
Ohio
Pennsylvania
South Carolina
Tennessee
Virginia
West Virginia
D.C.
Since I purchased my car in 1995, I have driven it to 48 states (all except Alaska and Hawaii.) Forty-six of these have been visited at least twice; forty-two were visited at least three times. The least-visited states (in that car) are Alaska(0), Hawaii(0), Florida(1), Minnesota(1), Arkansas(2), Washington(2), North Dakota(2), and Oklahoma(2).
Counting trips with or without my car, I have spent at least one night in every state since 1995. My last one was Hawaii, which I visited in April.
I have been to Alaska and Hawaii once each; I have been to all the other states at least three times.
I have been to about 1,600 counties in the United States, or about half of all U.S. counties. I have been to EVERY county in the states of Arizona, California, Colorado, Connecticut, Deleware, Maryland, Nevada, New Hampshire, New Jersey, New Mexico, New York, Oregon, Pennsylvania, Rhode Island, Utah, Vermont, and Wyoming. I am missing one county in Washington and Massachusetts and about five in Virginia.
All of this travel originated from Virginia. Maybe I travel in the U.S. too much. I need to see more countries…
Including drive-throughs (bold = not just a drive-through):
Indiana
Illinois
Ohio
Michigan
Wisconsin
Kentucky
Pennsylvania
Maryland
Virginia
North Carolina
Tennessee
Missouri
Oklahoma
Texas
West Virginia
California
Florida
D.C.
(Add Colorado, New York, and Georgia when you want to count layovers.)