From the Historicon website:
HISTORICON is the historical miniatures gaming convention in the United States. Each year, thousands of avid gamers enjoy what the New York Times has described as the "mother of all wargaming conventions." There will be hundreds and hundreds of games, the world's biggest wargame hobby shop, painting events, seminars, and much, much more. Don't miss the fun! Make plans now to attend HISTORICON July 8-11, 2010 at the VFCP in Valley Forge, Pennsylvania, USA.
Better yet, go early and visit Gettysburg for their three-day commemoration of the Battle of Gettysburg just a few days before, July 1-3rd. Take tours and participate in historical reenactments before you hit the biggest wargaming convention in the US.