Matt.H
Adventurer
You can legally carry firearms into National Parks (excluding certain administrative areas and buildings).
Some states have a requirement that you have a resident/non-resident permit from their state to do so. So even though you do not need a license to carry in Maine you do in some parks and state property. Be careful out there.
About Maine, from the National Parks Service.
• A permit is required to carry concealed
weapons. Some concealed-weapons permits
are recognized in multiple states, but many
are not. It is the gun owner’s responsibility to
know and understand what laws apply.
https://www.nps.gov/grca/learn/management/upload/Firearms-in-IMRparks2-2010.pdf