You can find out who owns a particular house or piece of vacant land through public records at the local county courthouse or online via its website. You can also work with a residential or commercial real estate agent and have them do the research for you.
To search in your area, simply look at your county's website. Most larger counties now have all their public record documents available online for your viewing. It is generally free to look at, but some counties charge a small fee to print copies.
You will need either the physical address or the property identification number to look up the information you need. The available information varies from county to county as well as from state to state, but it should include current and previous tax bill amounts, whether that tax bill is paid or not, the legal description of the property, the approximate lot dimensions, the square footage of any permanent buildings, and any lien holder information.
Depending on how detailed the county's system is, you may also be able to access past building permits, as well as copies of the current owner's lien paperwork. Knowing how much someone put down on their house or if they are late on their taxes can help you in your negotiation process.