Pickering Township was settled very early in the 19th century. At that time it was located in York County in the Home District of Upper Canada. Ontario County was established as a separate county in 1852. Pickering faces Lake Ontario and on its west it is adjacent to Scarborough Township, the easternmost part of the City of Toronto.
Until 1940 it was a rural township which included a number of communities of varying size: Dunbarton, Pickering Beach, Whitevale, Claremont, Brougham, Altona, as well as the village of Pickering itself. As part of the WW2 war effort, a large ammunition factory was built to the east of the centre of the township. This obliged the construction of a town that was named Ajax. At the end of the war the factory site was used first as an engineering school within the University of Toronto, and then as the home of various industies, some of which continue to this day.
In 1974, in a major municipal reorganization, the County of Ontario, in which Pickering Township was situated, ceased to exist. A new "regional municipality" was established, comprising of most of the former townships of Ontario County and some from Durham County, the county to the east. The new administration is called the Regional Municipality of Durham, or more often, Durham Region.
In the reorganization Pickering Township became the Town of Pickering, and in 2000 the City of Pickering. Its population at the 2011 census was more than 88,000. The original Pickering Village, however, is now located within the neighbouring Town of Ajax.
This drawing from Wikipedia shows the City of Pickering adjacent to the other municipalities of Durham Region. It can be compared with a similar map from Ontario GenWeb illustrating Ontario County prior to 1974.
For more information, see the EN Wikipedia article Pickering, Ontario.
The primary source for basic documents (vital statistics, land records, wills) for people who lived in the Province of Ontario is the Archives of Ontario, 134 Ian Macdonald Blvd, Toronto, Ontario, Canada M7A 2C5.
Civil registration did not begin in the province until 1869. Before then there may be church records of baptisms and burials. For the most part these are still held by the denomination who recorded them. Copies of marriage records made pre-1869 had to be sent by individual clergymen to the registrar of the county in which the marriage took place. These marriage records are available through Ontario Archives, on micorfilm through LDS libraries, and on paid and unpaid websites, but because they were copied at the registrars' offices, they cannot be considered a primary source.
Vital Records after 1869
Birth, marriage and death registrations are not open to the public until a specific number of years after the event occurred. Births to 1915 are now available [October 2014]; dates for marriages and deaths are later. Birth and death registration was not universally carried out in the early years after its adoption. Deaths were more apt to be reported than births for several years. The more rural the area, the less likely it would be that these happenings were reported to the authorities.
Land Records and Wills
Information on how to access land records and wills is best sought on the Archives of Ontario website. An ancestor's land holding might be found on Canadian County Atlas Digital Project if he was in occupancy circa 1878.
Association for the Preservation of Ontario Land Registry Office Documents (APOLROD). A list of Land Registry Offices for all Counties of Ontario.
The original censuses are in the hands of Library and Archives Canada, known to Canadians as "LAC". Copies of original microfilms are online at the LAC website for all censuses up to 1911. Each census database is preceded with an explanation of the geographical area covered, the amount of material retained (some census division material has been lost), the questions on the census form, and whether there is a name index. Census divisions were redrawn as the population increased and more land was inhabited. The 1921 census is only available through Ancestry.ca, but it is free-to-view.
E-books and Books
Some websites with more local information on Ontario County