Of 137 people who made landfall and stayed on in Plymouth (102 from the Mayflower and 35 more from the Fortune), 54 died during the first year. The mortality rate for settlers arriving that first year was nearly 40 percent.**
Population Dynamics for the Plymouth Pilgrims November 1620 - November 1621
|Atlantic Voyage||Docked off Cape Cod||Dec 1620 - Mar 1621||Apr 1621 - Oct 1621||Nov
What's perhaps even less well known is that an epidemic of plague, which decimated the Wampanoag tribe between 1616 and 1619 may have been responsible for the tribe's willingness to assist the settlers.
The epidemic wiped out an estimated three quarters of the Wampanoags who lived near Plymouth in the early 1600s. The tribe was estimated to be approximately 8,000 people in 1600, but fewer than 2,000 survived by 1620.
Without help from the Wampanoag, there is little doubt that the mortality rate for the Plymouth Pilgrims would have been much higher.
University of Illinois, Department of Anthropology. "Population Of Plymouth Town, Colony & County, 1620-1690."
Edward T. O'Donnell. "Of Plague and Pilgrims: How a Devastating Epidemic Shaped the First Thanksgiving."
*Declared a national holiday in 1863.
**If we use current techniques to estimate crude mortality rates - taking the number of deaths and dividing by a reference population estimated as the average of the beginning and ending date populations, the crude death rate was a whopping 577 deaths per 1,000 population.