I live out in the county, too, and if your county is anything like mine it includes biker gangs, drug cartels, drunk rednecks, burglars, etc. etc. And law enforcement is off in another part of the county, or in town dealing with things there.
There is simply no knowing what you are looking at in that type of situation. To me, it sounds like they were looking for a drug house based on directions to the place. I'm just suspicious that way, though.
Call the cops first or simultaneously. Keep your vehicle or other cover between you and them. Having your weapon is fine, keep it out of sight in order not to provoke, but ready to respond. ALWAYS cover first, don't try and outdraw somebody in the situation you described, there could be others in the car already trained on your position. Angle at the vehicle from a rear quarter, it's the most difficult for them to get a sight picture and requires them to be in an awkward position. Remain on your own property above all else. Don't go out in the street unless a violent crime is already in progress.
A camera, a phone, or my favorite, a 3 million candlepower spotlight does wonders. If they understand you are in communication or able to record their faces or license, they must decide whether to escalate or not, and you can think one step ahead.
I like the spotlight because it lets you look it over, lets them know you are curious and aware of local activity. And if it comes to a gunfight, they'll have a hard time seeing anything.