I spent about an hour going through the radioreference database and found this information: "
In MA there are 3 communities, Haverhill, Lawrence, and Springfield that use encryption on a fulltime basis; and 4 communities, Lowell, Methuen, Brockton, and Holyoke that use encryption on an 'as needed' basis. Boston uses encryption for it's Command Staff communications.
So, only 3 out of MA's 351 communities use encryption and 4 others use it on an 'as needed basis.
BAPERN (Boston Area Police Emergency Radio Network) does have a variety of tactical frequencies that can be encrypted.