OK, I went to my map collection and here is what I think is the best list I can come up with:
1A Pecatonica ("Rockford") Now District 17, last noted in 1974
2A Chicago (Harlem/Irving) Was and then again District 3. (2A only shown on the 1963 and 1964 maps)
5A Peru, later LaSalle-Peru. Now District 17 at LaSalle, last noted 1980
6A Ashkum, now District 21, last noted 1984
11A Litchfield, now District 18, last noted 1980
12A Carmi (Was Albion prior to 1978) Now District 19, last noted in 1980
13A Cairo, last noted 1988, now at Ullin
14A Pittsfield, now District 20, last noted 1982
17C Crestwood, Only noted on the 1978 map
17D Des Plaines, only noted on the 1978 map
The District 17 moniker for the combined District 3 & 4 was used more for sending teletype messages as using the "L17" identifier allowed messages to be sent to all terminals in Cook County. I was dispatching from 1979 thru 1984 and recall using L17 dozens of times. I don't think they ever actually merged posts or dispatch operations as Crestwood and "Chicago" always had different low band and high band channels, even during the District 17 days.
The Des Plaines post at the time was 477 River Road, now used by the ICC Police. After the State Police moved radio back to Harlem and Irving this was used for IBI (later called DCI) dispatch. I dated a dispatcher there for a while and visited the post several times during the late 70's and early 80's.
As for the 8A I mentioned in an earlier post, I was mistaken, it was actually 5A as BessieDawg mentioned.
As far as the sub-posts identifying with "XX-A" I think that was a discretionary thing with the posts as I have heard them use both the sub-posts city names and "XX-A" at different times. 13-A at Cairo used "Cairo" as often as not, as did Ashkum (6-A)
