The EDACS system operates as 3 distinct systems with certain (Police & Fire) groups simulcast between 2 zones.
Halton Hills is comprised of the towns of Acton & Georgetown. Milton is simply Milton. These 3 towns make up District 1, as defined in the database here and on the EDACS system when you listen to HRPD. PD units called "Alpha x" are Acton cars, "Golf x" are Georgetown cars, and "Mike x", "North x" and "Derry x" are Milton cars. And before my logic is question, yes, you will hear 3 district PD (see below) calls on the 1 district frequencies. To cover north Burlington the 1 district tower just west of Milton on the Niagara Escarpment simulcasts the Burlington PD traffic for radio coverage reasons.
"2 District" is Oakville and "3 District" is Burlington, again by Police districts and EDACS system programming definitions.Oakville & Burlington have their own Fire departments, but share dispatch duties, hence the patches you'll see between 2 & 3 districts.
On the other hand, Milton has it's own Fire department which encompasses Milton proper (2 stations for now) plus Campbellville (1 station). Halton Hills has 1 Fire service but 2 'districts', Acton being what they call District 1 and Georgetown being District 2. Both Milton and Halton Hills page out calls on 154.160, but use different pager tone combinations. They also have their own talk groups on the EDACS system.
Hope that helps!
Bob