plymouth rock is an american historic site in plymouth, massachusetts. people say the "mayflower" pilgrims there in 1620. but, they may not have. edward winslow did not mention the rock in "mourt's relation" (1620–1621). william bradford did not mention it in his journal "of plymouth plantation" (1620–1647). the first written reference to the pilgrims landing on a rock is found 121 years after they landed.