Sounds kinda like my afterprom that I hosted. We lived kinda in the middle of nowhere and had an empty granny suite on our house with 2 bathrooms, 2 bedrooms etc. so I thought it would be a good place for afterprom. This was 5 years ago, so before people around here used facebook.
I left prom a little early so I could get there in time before everybody showed up, but when I got there there was easily a few hundred people there, I barely knew any. The road had cars parked at least half a km, and they had fires started, some on the driveway that I had to almost drive over to get to the house. Of course, once afterprom had ended and the party had officially started it only got bigger.
When you live in a small town, word travels fast and when there's a big party everyone shows up.
I just got drunk fast and had a good time. Luckily nothing really got broken, I think just a planter and maybe a door.
Ever since then, all the afterproms have had parents watching who comes and goes, collecting keys, etc.