There are also 2 smaller airports that you can look into. Worcester Airport in Worcester, MA and Manchester Airport in Manchester, NH
You will find your most options at Logan International in Boston. The drive is about 1 hour and 45 minutes to the fairgrounds, straight out route 90 from Boston, all the way to Springfield.
The closest airport serviced by most major airlines. Bradley is just 20 minutes away from the fairgrounds of scenic route 75.. NOTE that Alaska Air does not service Bradley
Albany Airport is about an hour and 40 minutes west of the fairgrounds off of route 90.
Like Logan, TF Green is about an hour and 45 minutes away from the Fairgrounds.
There are 4 major airports within 100 miles of the fairgrounds.