You're exactly right.
Results of all night recording:
155.7375, DCS 664
154.385, CTCSS 146.2
151.115, CTCSS 100.0
154.86, CTCSS 156.7
If you can tolerate the periodic Morse code call signs, it's probably better to monitor Polk County without any tone squelch, because they do change tones fairly often.