You should have a county auditor site. Type in your county name with "auditor" and the page should come up. It will be a .gov listing. A map site called "cagis" will show you the boundaries of it.
We're under contract to buy a house, and I was able to glean a lot of information about it before we even went to see it. I knew where the property lines went, what was around the area, how the house was really situated on the lot.
The lot next door to this property is empty, and our first thought was "buy it!". The house that was there burnt down some years ago, and it's just been sitting. With the house number, we can type that into the auditor site by street name, and get a current name and address to the deed holder.
Oh, and it will also list the tax assessment value. Look in zillow or similar site to see what lots of the same size have sold for in the area. That way you can come up with a fair price to offer.
Be aware there are certain tax write offs for owning property like that, and some owners may not be willing to part with it. Just depends on their situation.