Cartwright was an inland, or back, township in the County of Durham. When Durham Region was established in 1974, Cartwright was merged with its two neighbouring townships in Ontario County under the name Scugog.
This drawing from Wikipedia shows the Scugog 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 most important centres of population within Cartwright are Blackstock (formerly Williamsburg), Caesarea--a port on Lake Scugog, and Nestleton--a station on the Canadian Pacific Railway.
For more information, see the EN Wikipedia article Scugog, 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 1914 are now available [October 2012]; 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. All of the original census (1851-1911) images are online with the exception of that for 1861. Not all of them are indexed. Later censuses are not yet available. Census divisions were redrawn as the population increased and more land was inhabited.
E-books and Books
NOTE: The OnGebWeb page for Durham County leads to further pages describing the townships of the county. The author expresses a worry that documents that had been in the care of Cartwright Township before the merger have not been found since that date.