I am looking for my son's 2017 ilinois tax refund and cannot find it in the previous taxes tab. Can you help?

Since you're using the online version, remember that you can only do one return per online account. So if you prepared/filed your 2017 return and your son's return with the online version of TurboTax, you're probably checking in the wrong online account.

or did you use the same account for both.  there can be only 1 return per year per account.  so using the same account for 2 returns would resulting in the destruction of the first return prepared.