The nearest post office outside Fermilab is located just off Batavia Road, east of Rt. 59. It's on the right-hand side, if you're heading out from the lab, about a half block before Butterfield Road (word of warning here: the post office comes just around a blind corner, so watch carefully for the sign by the road). For sending packages, you can find a UPS place just south of Batavia Road on the east side of Rt. 59, right next to the White Hen Pantry.