How do you distinguish property lines after a county road has closed , and who gets what? Our neighbor had a surveyor come out and has taken total control of the old road and has a sign posted that claims as much at the entrance to the road.

Get your own surveyor, and demand to see a copy of his survey.
Old deeds and old surveys are often so inexact that I've known people who ended up in court and were told they had to split the difference. At least here in New England, where boundaries were often a tree, fence post, rock or brook.

First the land may still be just that a closed road, The ownership of that does not automatically change over to anyone. Or it may go back to the first owners of the land where the road was taken from.

It will take a very detailed deed search and review. And of course where the survey company got their info, since they don't do need deeds, merely survey existing deeds.

how do you distinguish property lines after a county road has closed , and who gets what? our neighbor had a surveyor come out and has taken total control of the old road and has a sign posted that claims as much at the entrance to the road.

Did the county vacate the right-of-way, or merely close the road? Vacation means that the governmental authority would give the property back to the adjoining property owner(s).

Was the road between two or more pieces of property? If so, and if it was formally vacated, it would go to the adjoining owners, alng the centerline of the former road.

Finally, if it was an easement, as opposed to fee simple dedication as a roadway, the owner of the property subject to the easement can post it, since doing so would not impair the easement, which is no longer being used by the county anyway.