Inspired by this thread.
You have to have had a foot on the ground in the state, and that ground has to have not been an airport. Riding through a state without getting out of the car, bus, or train does not count.
If you picked ‘other’ please explain what sort of strange scenario I had not envisioned you’re talking about.
Six.
New Mexico
Arizona
California
Texas
Idaho
Pennsylvania
EDIT: If everything goes according to plan, Ohio will be added to the list in early August.
I’ve been to all of them, save Alaska and Hawaii.
My dad used to be an interstate trucker, and I spent a good bit of time riding with him, especially before I started school.
12
Arizona, California, Colorado, Kansas, Missouri, Nebraska, Nevada, New Mexico, Oklahoma, South Dakota, Texas and Utah.
Damn. I didn’t even get to spend ten minutes as the person who’d visited the most. 
I had to write it down to remember.
New York
Pennsylvania
Tennessee
Rhode Island
Mass
Vermont
New Jersey
Michigan
Illinois
Colorado
California
Virginia
West Virginia
Ohio
Florida
Indiana
Kentucky
I think that’s it. I’m still not convinced Delaware exists.
I did too. And I needed a map.
I voted other, mainly just because I could. 
The story is not so great though.
Whenever “how many states” comes up, I usually diligently start rattling off states and counting them, but then someone (Mom, sibling, husband, etc.) will invariably start adding to my list saying that I was in whatever state for whatever reason, or on whatever trip that I have completely forgotten about.
It’s much easier for me to list states that I remember having been to and/or having lived in (not counting airport stops or drive-throughs which would bring my list pretty darn close to 50) which are in no particular order:
(1) Maryland
(2) South Carolina
(3) Georgia
(4) Tennessee
(5) Virginia
(6) Ohio
(7) Illinois
(6) Missouri
(7) Kansas
(8) Nebraska
(9) Arkansas
(10) Oklahoma
(11) Texas
(12) Colorado
(13) California
(14) Arizona
(15) New Mexico
(16) Nevada
(17) Utah
(18) Kentucky
(19) Guam (territories count as states, right?)
(20) Hawaii
(21) North Carolina
(22) Indiana
(23)Alabama
(24) Iowa
ETA already…(25) Louisiana
whew…I think that’s all, but someone will probably be along to remind me about a wild weekend I spent someplace that I have blocked from my mind. And as I said, if I got to count airport stops or just driving through places my list would be much more complete. 
I think it’s 21, because we normally drive through the US, and we get out and use the bathroom and stop for gas and food. There might be one or two that we just drove through.
Wow. Half of them.
Maine
New Hampshire
Vermont
Massachusetts
Rhode Island
Connecticut
New York
Maryland
Virginia
North Carolina
Georgia
Florida
Pennsylvania
Ohio
Indiana
Illinois
Iowa
Minnesota
Missouri
Kansas
Utah
New Mexico
Idaho
Washington
California
I voted “41-45” but I miscounted. It’s actually 46. I work for a Federal agency that has a regulatory presence in 49 states, and I travel quite a bit for work. Plus, from my personal history–it adds up to just about all of them.
The ones I haven’t been to are:
Hawaii
Maine
New Hampshire
Vermont
There have been a few days when I was in MA, then RI, then MA, then RI, then MA, then RI, then MA, then RI, then MA, all in a few hours. The road to someone’s house crosses the state line a couple of times. I had to ask the owner of the house what state we were in. When he said MA, I asked where the state line was. He said “You see that house across the street? It runs through his living room.”
Editing time has passed, but hubby just reminded me (as I said he would…) that we spent a weekend in (26) Mississippi.
Think I’ve been to all states except Maine, California, Hawaii, and Alaska. I’ve also either caught fish, gone fishing, or at least gone camping in most states.
36, although 2 of those I just drove through. (The other 34 I had actual destinations where I spent time).
Also, D.C., Puerto Rico, and the Virgin Islands.
–Cliffy
Every one but Florida, Mississippi and of all places Hawai’i. :o
Maine, New Hampshire, Massachusetts, New York, New Jersey, Delaware, Maryland, Pennsylvania, Ohio, Virginia, West Virginia, Michigan, Indiana, Kentucky, Illinois, Tennessee, North Carolina, South Carolina, Georgia, Florida, Missouri, Minnesota, Arkansas, Louisiana, Texas. That’s 25. Kansas is in the “doesn’t count because I was in the hotel shuttle on the way to the airport” category.
15: Kentucky, Mississippi, Tennessee, Louisiana, Alabama, Georgia, Florida, Missouri, Indiana, Ohio, Illinois, Michigan, Virginia, West Virginia and Maryland.
32:
California, oregon,washington, idaho,colorado, utah, arizona,new mexico,texas, florida, south carolina, georgia, north carolina, virginia, maryland, west virginia, tennesee, pennsylvania, new jersey, delaware, new york, connecticut, massachusetts, vermont, new hampshire, maine, rhode island, illinois, ohio, indiana, kansas, arkansas