What is Bills Of Mortality?

Legal Definition
Bills of mortality were the weekly mortality statistics in London, designed to monitor burials from 1592 to 1595 and then continuously from 1603. The responsibility to produce the statistics was chartered in 1611 to the Worshipful Company of Parish Clerks. The bills covered an area that started to expand as London grew from the City of London, before reaching its maximum extent in 1636. New parishes were then only added where ancient parishes within the area were divided. Factors such as the use of suburban cemeteries outside the area, the exemption of extra-parochial places within the area, the wider growth of the metropolis, and that they recorded burials rather than deaths, made their data invalid. Production of the bills went into decline from 1819 as parishes ceased to provide returns, with the last surviving weekly bill dating from 1858. They were superseded by the weekly returns of the Registrar General from 1840, taking in further parishes until 1847. This area became the district of the Metropolitan Board of Works in 1855, the County of London in 1889 and Inner London in 1965.
-- Wikipedia
Legal Definition
Accounts of births and deaths which have occurred in a certain district, during a definite space of time.
-- Bouviers Law Dictionary