From looking at the frequencies used in Cullman county, depending on what you want to listen to, you would need up to 3 sdrs to cover the 151-159 mhz range of the p25 systems that is used in the county, since a regular rtl-sdr only covers a 2.4mhz range at a time. To cover all the P25 & NBFM channels, probably 4 sdrs.
I also recommend SDRTrunk.