I'm just barely staying ahead of Andrew. Here's the additions to my post #15 above.

Arizona
Manzanita 1/3 D Sprint (R)
** This is one I had forgotten. It's the 1/3 that was inside the 1/2. Does this count?
Connecticut
New Haven Coliseum 1/6 P TQ
** Another forgotten one from many years ago.
Illinois
Belleville 1/5 D Midget
Lincoln 1/4 D Midget
Quincy 1/4 D Midget
** These were during 2014 Illinois Midget Week.
New Hampshire
Canaan (Fair) 1/4 D Sprint, Mod
** This was 2 years ago, during the track's last season.

Now I'm at 161 tracks in 25 states, Canada, and England.
I saw Sprints, Midgets or Dirt Champ cars at 149 of those tracks.