Rhode Island Tercentenary Issue First Day Cover
300th Anniversary of the Settlement of Rhode Island
Issued on May 4, 1936 in Providence, RI - Scott #777

Unofficial Town Cancel - Westerly-Misquamicut Summer Station
1st John Kilton Cachet - Planty #777-61k

The Misquamicut Post Office was a sub-station of the Westerly Post Office and operated from October 1, 1928 to June 17, 1975. This Post Office operated during the summer only and its first day of operation each year was on June 1. Thus, the first day that the tercentenary issue could be canceled at this post office was on that date and counts as an unofficial city first day cancel.

Sources:
Check List of Rhode Island Post Offices 1790-1994 - Del Beaudreau
Rhode Island Postal History: The Post Offices - Merolla, Jackson & Crowther