I visited the J& P National Motorcycle Museum in Anamosa, Iowa, a few weeks ago, for the first time, but not the last. I think it's one of the great motorcycle museums, on a status with the AMA museum in Columbus, Ohio.
About 400 bikes, including several Brough Superiors and five or six Vincents, including the only "Black Prince" Vincent I have ever seen. The pre-1920 bikes are there in a great amount, both original condition and restored.
I recommend a visit to this museum to everyone interested in motorcycle history, and motorcycles of any nation.