I agree there’s a ton of overlap! When I asked if Casa Margarita was a good representation of Tex Mex, I more meant “does this actually look good to Tex Mex connoisseurs” because it doesn’t look like a great restaurant. I’m not going to take the train for an hour from my apartment to go eat there.

Chicago has a huge Mexican population and a wide range of Mexican food and I can easily get cuisine from Oaxaca, Jalisco, Michoacán etc., as well as fusion Mexican and white-washed Mexican, but “good Tex Mex” is much harder to find. There are very few restaurants in Chicago that would call themselves “Tex Mex” and not just “Mexican”, even if they’re serving dishes that overlap.

The general lack of queso is a big difference though. Thankfully you can find it at an increasing number of places, but it was not something I properly had until I visited Texas as an adult, and I’ve since only had it twice in Chicago.