The 6-cent stamp honoring the seventeenth century explorer Father Jacques Marquette was issued September 20, 1968, at Sault Sainte Marie, Michigan, where he established in 1668 the oldest permanent settlement in that state.
The stamp was designed by Stanley W. Galli and was issued in panes of fifty, with an initial printing of 120 million.
Reference:
Postal Bulletin (August 8, 1968).