In Minnesota we now have or will soon have five F18s, I believe there is a sixth but I am not in touch with that one so a I can't confirm.
In Wisconsin there are seven total, four of them actively raced. (one cabin boat, one semi retired, two with the same owner)
Last year in Iowa there were two, however, one may have been sold, and the other maybe for sale (aren't they all).
There are at least two in Northern Illinois. Don't believe any F18s are down in the St Louis area anymore.
That's a potential grand total of 17, not bad when you consider four years ago there was only one!

Michigan and Indiana has a number of boats, hard to get a handle on the exact numbers. I would estimate 6-10 racing at least occasionly in that area.

And this is a true formula fleet of boats with Hobie, Nacra (all three versions) and Capicorn all represented.