It depends on what you mean by smart. Having an education doesn’t mean you have common sense. Having a college education doesn’t mean you will score higher in an IQ test than someone who doesn’t have a college education. I too know some college educated people who are completely lacking in common sense and practical skills. They may be brilliant in their field, but beyond that – forget it.
As has been pointed out, there are some great examples of individuals who didn’t go to college and have been incredibly successful in their fields. People like Bill Gates and Richard Branson are extraordinary though. They aren’t the norm. Still, there are many successful, average people who haven’t attended college.
However, as @LuckyGuy has suggested, research shows those with a college education will generally end up earning more than those who do not. Not always, but research suggests they’ll have a higher earning power and less unemployment.
My own experience (and I work in the university sector) is that a college education changes the way people process information. Not always of course, but I have witnessed students becoming more critical and developing a more questioning approach. They may become less likely to accept generalisations and to take a more evidence-based approach. This isn’t always going to be the case but I do think a college education forces people to seek evidence to back-up their assumptions. Does it make them smarter? No. However, it quite likely makes them more critical of information and ideas. In some fields of work, the theory and knowledge acquired at college, when teamed with hands-on experience, is likely to produce more proficient employees than the person who only has hands-on experience. They may leave college as novices when it comes to their hands-on skills, but when they acquire those skills, they have both theoretical knowledge and the practical expertise.