I can think of nowhere in the US without Mexican food options, and I think that is a good thing.

I love Mexican food and think the spread of Mexican cuisine enriches our culture. Hard to believe that at one point Italian food was considered "ethnic" but is now one of the most mainstream types of food available in the US.

I presume that to find a town in the US without a Mexican restaurant, that town would have to be exceptionally remote and probably lacks other conveniences besides Mexican food.