Chowhounds have plenty of tricks—some traditional, and some original—for making their chili nice and thick. danhole says a couple hours of simmering does the trick. Several recommend using masa harina (flour for corn tortillas) mixed with water; Will Owen mixes about a third of a cup with enough cold water to make a runny gruel and adds it to the simmering chili. tzurriz crumbles up and adds some tortilla chips (or just throws in a tortilla or two) and lets it simmer. The tortillas will dissolve and thicken the chili at the same time.
Davwud mashes some of the chili’s beans to help thicken it, while sheilal uses refried beans, and says they don’t alter the flavor much but thicken nicely. mamaciita has used canned pumpkin to thicken turkey and black bean chilis, and grrlscout adds mashed cooked sweet potato.
Board Link: How to make thicker chili?