There are few Maryland sites in the DB:
FirstEnergy Trunking System Profile
www.radioreference.com
As far as programming talkgroups, there aren't that many known (and likely aren't that many overall). It would probably be best to program in whatever is of interest that is in the DB and then add a Group Wildcard (GRE / Whistler) or enable ID Search (Uniden).
Depending upon the RTL that you have, it could be significantly off -- some of the much older dongles simply don't have a 0.5 ppm TXCO and many of them run so hot that they drift wildly until warmed up.
Instead of tuning to a specific frequency, tune to the center of any actual signals you find -- and then if it's P25 and you're using DSDPlus or Unitrunker, the site info should pop up.
And if you are just using Unitrunker and an RTL, and you think the RTL might be "off", then run SDR# and look around the band and find known signals and see how far off it is. If you don't have DSDPLus, that's a good thing to use when sleuthing out things like that.
Mike