Where is a good place to live in southwest Illinois?

You need to be a little more specific. Do you want to be within commuting distance of St Louis or any other specific place, or do you just want to live somewhere in the general area?

If you are looking for some place within commuting distance of St Louis, most of St Clair County is OK, as long as you are east of IL 157 (ie avoid East St Louis, Cahokia, Alorton, Brooklyn, Washington Park, etc). O'Fallon, Shiloh, Mascoutah, Lebanon, and most of Fairview Heights and Belleville are good places, along with the rural areas in the southern part of the county. Those areas are also good if you want to be close to Scott AFB.

For Madison County, just generally stay clear of the areas near the river, especially in the SW part of the county.

The rest of SW Illinois is pretty rural.

I like Cape Girardeau. Nice place, nice people, by the water and plenty of sites and jobs. Cost of living is moderate.

In the middle of nowhere.