This was interesting…
When I was trying to decide where to move to in the US, one of the factors I looked at was “educational attainment” of the states, that is, what portion of the residents of the state have completed what levels of education. I used data from the 2000 federal census.
At the time, Vermont came in first (for my purposes), and New Hampshire came in second.
In the following link, IQ scores, educational attainment, exam scores, etc are used to determine the “smartest” (not necessarily the highest IQ). New Hampshire is second, Vermont third.