success! I ended up using corn meal as some of you suggested and it did work! I have a feeling I'd like the taste of tomato paste more, so next time that's what I'll substitute instead of all tomato sauce. Here's a pick of the finished result! Thanks so much for all your input!

Thanks everyone! I'm gonna try tomato paste first, then corn chips second. :)

If it's bean chili, you can try mashing some of the beans, or adding 1/2 cup or more of mashed beans to the chili. And I like the simmering and tomato paste idea too.

The corn meal/flour option is the best. Even ground up tortilla chips (not much, you will only need 2-3 tablespoons of corn meal per pot of chili) will work in a pinch. If you have regular corn meal (like you use for cornbread), that will work as well. Tortillas, chips or the meal can be ground pretty fine in a processor, that'll give you an approximation of the masa harina.

Do what onetribegourmet says. I keep a tube of tomato paste in the fridge just for occasions such as this because this used to happen to me all the time; since learning the tomato paste trick, it hasn't happened once.

I remember one time when I was in a hurry to get dinner on the table and the chili was like soup, so I boiled up some elbow macaroni and threw that into the chili pot. The kids loved it. I didn't. But they clamored for "chili soup" quite a few times after that.

Another time, I strained the liquid out and boiled it down. That wasn't a wonderful experience, either.

This might be a new one to you but having quinoa FLAKES on hand and sprinkling them in the chili might thicken it up a bit, the flakes pretty much dissolve. Likely you don't have them hanging around your house, but for future use?

Make a slurry with masa harina and mix it into your chili

You can continue to simmer for a bit longer but do add a tablespoon or so of tomato paste, that should thicken the chilli.. I hope that helps! :)

If you have corn tortillas, you can tear them into the chile and they will dissovle and thicken it eventually (or blend them with a little water first.) Or as you suggest, put it on a fast simmer so excess liquid evaporates.