Always said Carter was the smartest

Carter has common sense and an inquisitive nature. His genius is in making the connections between people, projects and observed phenomena. He also has a healthy streak of humility to temper his ego. The scientists in Eureka often make mistakes because their egos revolve around their belief/knowledge they are brilliant, educated, have high IQs and multiple degrees. When the observed phenomena disagrees with their theory they dismiss it because their egos tell them they cannot possibly be wrong.

Carter expects to be wrong. That's why he constantly runs his ideas by other people and asks questions. He's looking for the right answer with no preconceived notion that he is the only one that has it.

One of the first things I ever learned in college is that the truly brilliant people freely admit they don't know all the answers. Being smart isn't about always knowing the right answer. It's about knowing the right questions to ask.

As Holly said, the townspeople are all smart, but it's Sheriff Carter who's the strong force who holds them together.