Heat a large skillet over medium-high heat and brown the ground beef with the chopped onion until no pink is left in the meat. Do not discard the liquid if you are using lean beef. Add it to the crockpot as well. It will add more flavor to the soup.
Transfer the browned beef to the crockpot and add the chili beans, kidney beans, and whole kernel corn, each with their liquid. The liquids will add body to the soup and help thicken it a bit.
Add the diced tomatoes, tomato sauce, green chilies, and water to the crockpot as well.
Last but not least, add the spice mix and give everything a good stir. If you don’t have all the spices used, you can buy a packet of taco seasoning and use that instead.
Cook the soup on low for 8 hours or on high for 4 hours.