The deaths of plague victims were often marked with the letter P
Details of those who died from the bubonic plague in London will be among more than 18 million parish records to be published on the internet.
Dating back to 1539, these records will offer the only way to trace the birth, marriage or burial of a person living before 1837, ancestry.co.uk has said.
The records show victims of the plague in 1665 and 1666 were sometimes marked out only with the letter P.
Experts believe the project will hugely benefit family history research.
Thomas Cromwell, King Henry VIII's vicar-general, began the collecting of parish records.
The data also covers the Great Fire of London, which occurred in 1666 and caused huge destruction.
The records are being published by ancestry.co.uk in partnership with the City of London's London Metropolitan Archives and Guildhall Library Manuscripts.
Dr Deborah Jenkins, assistant director of the City of London's department of libraries, said: "Parish registers reveal facts about the lives of individual Londoners and their families, providing key evidence about shifts of population, disease, war and famine.
"This is a fantastic project that will transform family history research for those with ancestral ties to London."