Through the support of the Wellcome Collection, images of the Bills of Mortality from their library are available here to browse. The Wellcome Collection (text from Jessica) .
Rights to the images located here are CC-BY Wellcome Collection
Volumes of the Bills of Mortality from other libraries can also be viewed at Early English Books Online (EEBO). EEBO is a collection of books on microfilm and digitized, available through subscription services at many libraries or at the Internet Archive:
Early English Books, 1475-1640
Early English Books, 1641-1700
To better understand the numbering and dates of the Bills of Mortality, review this overview of calendars: