Thorah was established as a township in York County in the Home District of Upper Canada in 1820. The township was incorporated in 1850 and transferred to Ontario County upon its formation in 1852. The Village of Beaverton, originally part of the township, was incorporated as an independent village in 1884.
Part of the Trent-Severn Waterway was constructed through the northern portion of the Township and opened in 1907.
This drawing from Wikipedia shows the enlarged Brock Township 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.
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