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Has the depth for deck footings changed from 3 to 4 feet in MA?
Call the building department -- they have that information.
I'm in RI and mine were required to be 40" below grade so I would think it would depend on where you are in MA. If you are on the coast where it doesn't get as cold I imagine that the depth would be lower than if you were in northwest MA. As suggested check with your building department for their exact specs.