Presuming your GREs aren't a disaster, your chances are great. UIUC is one of the better ranked schools in the country for chemistry, 3.1 isn't a terrible GPA, you've been in the military (which is usually looked at as a desirable thing), and presumably you're American (which will also make you a desirable candidate). I'd say the majority of applicants also don't have more than 1 or 2 summers of serious chemistry-related summer internships, so if you spend your last summer getting some work experience in a lab, you won't be far behind at all.