I don't see anything in the statutes that requires any of the officers to be a Maine resident.  However, I would think it would be awkward for the Treasurer to be a non-resident, as I think the bank account should be local.  That being said, so much can be done online these days, as long as the officers can perform their duties, I don't see why they would have to be Maine residents.  But whoever does the duties of a road commissioner should be local so they see what's going on with road conditions.