First, I would record and Cite what information I found. Enter it AS I found it. What ever that may be.
I would then NO go by "I was told" something. I would do a little research to, again, document what I found. In this case, I would put that information and the source of that information, in the Note section for that Individual.
I have a number of these, and was able to locate the County Boundry changes over time. In my case, it was Parishes in Maryland. I also have a couple of ancestors listed as Kansas Territory.
I am using Family Tree Maker 2008 and want some of these individuals, with outdated locations, to appear on the Map feature of 2008, so I enter some Current information for Records Purposes and make a note in the entry as to what I was doing.