Michigan (where I live)
Ohio (Ohio State)
Illinois (primarily Chicago, another time UIUC)
New York (NYC)
Pennsylvania (Penn State)
Maryland (University of Maryland)
California (San Francisco, San Diego, Sacramento, Long Beach)
Nevada (Las Vegas)
Stopovers during plane rides:
States that I've just traveled through and never actually stayed in:
Virginia (very briefly)
New Jersey (on the way to NYC)
Kentucky/Tennessee (on the way to Alabama)
Total States "Visited": 20/50
I've also been to Ontario several times and Mexico City once after moving from the Philippines to the U.S. I'd be lucky if I ever traveled somewhere outside North America.
To anyone who's visited at least one European microstate: I am jealous.