Because Ontario was settled as an English, Christian country, many early records of genealogical interest are held by the churches. At first the Anglican and Roman Catholic denominations were the only "established" ones and so the only ones to hold official records, but it was not long before other denominations were allowed to perform marriages (starting in 1831) and to hold registers.
The same 1831 act required dissenting ministers to register all the marriages they performed with a Clerk of the Peace. Note that Anglican and Roman Catholic ministers were not required to register their marriages since they were established religions, not dissenting religions. The Clerk of the Peace was a district official, so the registers are known as District Marriage Registers. Some Anglican and Roman Catholic marriages are in the District Registers, usually from the 1840's. It is not unusual to find christening data in the District Marriage Register. The registers have been transcribed in a multi-volume set: Walker, Dan & Fawne Stratford-Devai – The Marriage Registers of Upper Canada / Canada West – Norsim Publishing (1998)
In 1850 Districts were abolished and Counties gradually took over their administrative role. The County Marriage Registers included marriages performed by all ministers. The County Registers began on January 1 1858 and lasted until civil registration began on July 1 1869. Of course these are the official dates; the reality has considerable flexibility. The registers have been transcribed in a multi-volume set: Hancocks, Elizabeth – County Marriage Registers of Ontario Canada, 1858-1869 – Generation Press (1990).
Locating Religious Records
Finding a church's registers can be a frustrating exercise since they could be housed anywhere, if they have survived to the present day. Libraries and Archives Canada have some, as do the Archives of Ontario. Many denominations have their own archives, which holds quite a number of records. Local archives and libraries hold some. A surprising number are still held by the individual churches. The OGS Branches have a long-term project of identifying the location of church records. See the Links page for a list of denominational archives.