I won't get in to too much detail here, but the counties you're asking about run a wide range of radio systems.
Bell County is using an analog EDACS trunking system and will be able to be monitored by all the latest generation digital scanners (RS Pro 106, GRE PSR-500 and the Uniden 396XT and HP-1).
Falls and Hill counties are mostly analog VHF, with a few UHF frequencies and the only P25 entity is Hillsboro PD.
McLennan County is a different beast. Most PD/FD (excluding Waco) uses analog VHF. Waco and McLennan County use their analog Motorola trunking system (except EMS which I'll explain in a minute). This system is very active and I'd estimate it will be replaced in the next few years for a digital system, though we're not sure which frequency range (VHF, UHF, 700 or 800 MHz). Most of the small municipalities will want to remain VHF, but I wouldn't be surprised to see Waco in 700 MHz. That being said, if they would all choose P25 systems they could be interoperable no matter what frequency range the system operates on. EMS uses the TxWarn digital trunking system, a wide area radio network that is mostly 800 MHz near you, but 700 MHz in other places.
DPS uses VHF P25.
In all honesty, to be as prepared as possible for whatever systems get implemented in McLennan & Bell counties in the next few years, I'd recommend looking in to the latest generation of digital scanners from each manufacturer. Peruse the scanner forums here and read the "versus" threads where users compare qualities of each.
Necessary options: needs to be a P25 trunking scanner, and it couldn't hurt to get one that scans the 700 MHz public safety band. There is no 700 MHz near you now, but that is the direction a lot of systems are heading.
Good luck, and let us know if you have any other questions.
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