Most likely yes. A good number of "larger" agencies have migrated to either P25 trunking systems or P25 conventional systems. However there are still a number of smaller communities that continue to use analog systems.
So it really depends on what you are going to monitor.
You can check the database reference section, looking up the state, then county of interest. It will show whether the system is P25.
Also whether you travel and do scanning is a consideration. It's a certainty that if you do, you will run across P25 systems.
With the FiRST statewide system coming on line (and/or if you happen to be in Prince George's or St.Mary's County), Phase 2 capability is all but mandatory. There are quite a number of scanners with this capability, and a couple with the capability of copying DMR / MOTOTRBO systems, which are also on a growth path here in Maryland.
See this article in our wiki - section 4.2 lists the scanners that are Phase 2 capable...