 On April 5 , 1621 , after being anchored for almost four months in Plymouth Harbor , the Mayflower set sail for England . Nearly half of the original 102 passengers had died during the first winter . As William Bradford wrote , " of these one hundred persons who came over in this first ship together , the greatest half died in the general mortality , and most of them in two or three months ' time " . By November 1621 , only 53 pilgrims were alive to celebrate the harvest feast which modern Americans know as " The First Thanksgiving " . Of the 18 adult women , 13 died the first winter while another died in May . Only four adult women were left alive for the Thanksgiving . 
