New York: New York City to Albany.
Hawaii: Honolulu to Maui, Maui to the Big Island, and back.
Washington: sightseeing helicopter at Mt. St. Helens
Florida: on a flight from Panama to Miami we were forced to do an emergency landing due to a hurricane at the Key West Naval Air Station, then continued to Miami when the weather cleared.
Alaska
California
Pennsylvania (Including British Airways Philly-Pittsburgh, extension of a flight from London)
Texas (including flights on a B-17 and a UH-1N Huey)
Utah
I forgot general aviation, which would add Florida, since I have taken a flight from Sarasota to a ranch near Orlando on a small plane.
Illinois (Peoria to Moline.) This was one leg of a trip to California–the plane stopped in Moline, then went on to Denver. Then we switched planes to L.A.
I’ve flown hundreds of times, but never from a city to another city all in the same state.
Washington
Minnesota
Wisconsin
Montana
West Virginia
I drove from Boston (my home) to Providence, and boarded a 727 to Chicago. The plane had a problem and we diverted and I wound up right back in Boston. Not the same state, of course, but a short flight for such a big plane.
Within 5 states:
California
Hawaii
Alaska
Arizona
Florida
I realize we’re not asking for this but just for grins I wanted to see, if it’s to and from then it’s 28:
California
Hawaii
Nevada
Washington
Alaska
Arizona
Texas
Ohio
Missouri
New York
New Jersey
Maine
Rhode Island
Massachusetts
Pennsylvania
North Carolina
Oklahoma
Louisiana
Mississippi
Georgia
Illinois
Colorado
Minnesota
Wisconsin
Utah
Florida
Indiana
Virginia
But my answer is 5 states.
California
Washington
Texas
North Carolina
Just Colorado, the little “hop” flight from Denver to Colorado Springs & back. You go up, you come down in under an hour.
Denver to Colorado Springs. I did that hop once and forgot that.
So it’s 6 states:
California
Hawaii
Alaska
Arizona
Florida
Colorado
Are non US subnational entities allowed?
Because then Punjab and Sindh count for me. Also England.(Newcastle to London).
Commercially I don’t think I have ever flown just between airports within a state.
The OP doesn’t specifically leave out military flights so in Army helicopters:
Alabama
Texas
California
Washington
New Jersey
Pennsylvania
Maryland
Virginia
Also several German states
Pretty sure Hawaii is the only one, although it’s vaguely possible that I may have had one that I’ve forgotten about, or was too young to remember (my family went to California and Florida when I was a little kid, and those are both states where you plausibly could take an in-state flight, I guess).
Airline: California, Hawaii, Ohio, New Jersey, New York
Private: Ohio, Massachusetts, New Hampshire, Maine, Rhode Island, Connecticut
Michigan. Flew from Detroit up to Marquette (in the Upper Peninsula) for a wedding reception.
4 that I can recall.
NYC airports to Syracuse and Syracuse
FL Miami to Orlando (odd transfer)
CA San Diego to LA, LA to San Fran
PA Philadelphia to Pittsburgh
Back when TWA was still an airline and they had a hub in St Louis, I used to do the KC - STL leg on just about every business trip I took.
As best I can recall …
CA, AZ, NV, WA, CO, MO, TX, OH, NY, FL, NC, VA
To the best of my recollection…none.
Every flight I recall making has been from one state to another.
More than I would have thought:
New York (between Rochester and NYC airports)
Washington (between Seattle and various cities in Eastern Wa)
Hawaii (Honolulu to other islands)
Alaska (Anchorage to Sitka, Sitka to Juneau)
Colorado (Denver to Aspen)
Texas (changed planes in Dallas on way to San Antonio)
Nevada (Vegas to Reno)
California (various)
Kentucky (Cincinnati airport to Lexington)