You guys may be missing the point. The OP said that Ingham County was rebroadcasting *JACKSON* Co Main Dispatch.
The only reason I can think of for them to do that is some type of cross-jurisdictional incident involving both Jackson & Ingham County units; a chase, K-9 track, or some other incident at or close to the county line.
It's also very normal for counties to have their vhf police dispatch to be also on Mpscs. This so msp they can transmit and receive the county radio traffic. That's the case of many on the p25 database and was also the case near me for Midland Bay Saginaw counties prior to then going P25. When they went digital those msp patched talk groups became the county police dispatch.
At SAESA we've already begun adding Motorola 800 radios to the department mainly to be used fot mutual aid EMS runs at this time but there has been talk at the county level of a future switch to the MPSCS system. Not sure on specific details though.