That would be Wright Patterson Air Force Base, just outside of Dayton, Ohio in hanger #27.
It was kept there for a while, but the crashed UFO is now under Wright State. You know all those tunnels they built under the University. The ET research facility is right below the tunnels, and strangely looks a lot like the facility in the Half Life game. ;-P
Note To Self: Remember to pick up supplies for a new AFDB ( http://zapatopi.net/afdb/ ). Current AFDB is saturated, and need to make a new one.