The Rattlesnake Island Local Post is a post at Rattlesnake Island in Lake Erie, Ohio, operated by James P. Frackleton, MD. This was the only USPO sanctioned private local post in the US. Issued 77 stamps from 1966-1989, only the first set was rectangular, when the USPO complained, they began using their famous triangular shape. One set of stamps were issued each year. One source of info is the book;"The History & Local Post of Rattlesnake Island Lake Erie" by John Wells. However, the post has been reestablished in 2005 with new issues not listed in the afore mentioned book, still continuing the triangular format. There is one elongated rectangular issue in 2004 with facsimiles stamps on each end stating "Rattlesnake Island, OH" valued .18C is questionable but know with Rattlesnake Island LP cancel. Watch for a tribute post, also called, Rattlesnake Island Local Post in Sun City, AZ issued 2 stamps in 2005. These are all rectangular and are photos taken right off and out of John Wells book.
I just found 6 stamps from a worldwide collection I purchased to get me started in the hobby. For some reason they were with Nicaragua! I was initially confused, but the Lake Erie on the stamp on google helped sort me out. I will try and take some pictures later.