I'm pretty sure that if the only thing you traced was the county outline, you'd be safe... I just had a similar issue with my Goat Island thread... and you can't *own* the shape of the land (from what I understood of the answers I was given)
However, if you want to be safe, county lines are a matter of public record, and the website for whatever city is the county seat should tell you how you can get a (non-copyrighted) outline/guide/whatever.
We had to get bunches of them for upgrades to the farm, and there were never any copyright things on the pages
EDIT: of course, you still have to add your own info to the map, in your own way... but you'd be doing that anyway, right?