Which US states have the highest Magic: the Gathering participation?
As one might guess it seems the states with the largest number of Magic players are also the ones with the largest populations.

I am assuming that the number of players in a state is directly correlated with the number of judges in that state. To get the number of judges in each state I used the WotC Judge Center tools to find all of the Level 1+ judges in the US that had a state listed (37 out of 3067 judges in the US didn't have a state listed).

The top 5 states by number of judges are (in order): California, Texas, Florida, New York and Illinois. These also happen to be the top 5 states by population (in the same order). Once you get past the top 5 only Colorado has the same exact ranking for both (#22), but most of the others are fairly close between the lists. You can find the data I used in this Google Sheets document.