
Emigration Records would refer to records of residents leaving Ontario to live elsewhere.
Not all immigrants who came to Canada came here to stay. Nearly half of all new arrivals were bound for the USA. In the early 1900's when the USA started limiting immigration, ship fares to Canada were cheaper than fares to the USA. It wasn't uncommon for someone to immigrate to Canada, stay long enough to save up some money (perhaps marry and/or have a few children), then move on to the USA.

These types of records are a bit different in that you won't necessarily find what you're seeking in Ontario - you'll need to look to the country or area that your ancestor emigrated to. For instance, if your ancestor left Ontario and settled in a U.S. state you might find their Naturalization records... in the U.S. state that they settled in. You likely won't find records of their emigration in Ontario.
If you're seeking an emigration record you likely already know that at some point your ancestor lived in Ontario, even if just for a short period of time. It's important to establish the time period that they were in Ontario, and if possible the area. Research that time period and area to learn why your ancestor might have left - also be sure to research the time and area where your ancestor emigrated to. There may not have been obvious reasons to leave where they were living but every reason to move to where they went (gold rush? free land? relatives?)
Border Crossings
Until the 1890's no records were kept of persons crossing the Canada-USA border. For those leaving Canada for entry to the USA records exist from 1895-1954. Records do not exist for anyone who arrived or left prior to 1908 or 1895.
Reasons For Emigration
Gold! In 1898 Yukon Territory experienced a huge influx of new 'settlers' after gold was found. Was your ancestor among them?
Natural Disasters: See our Disasters page for a list of some known disasters. If your ancestor lived in or near these areas perhaps they had no choice but to leave.
Land: In the late 1800's/early 1900's free and cheap land was offered in Northern and Western Canada as an incentive to encourage settlement. If your ancestor left Ontario during this time, perhaps they headed west to the prairie provinces.
Trains: This was a popular mode of transportation from the mid-1800's until travel by plane became affordable. Many trains would carry emigrants from Ontario to new homes in other parts of North America. If your ancestor worked for a railway it was common for families of the workers to travel with them, setting up camp where the railway was being built then moving on to the next station as construction progressed. When seeking rail records don't restrict your search to Canada - be sure to look at US records as well. Not all trains that operated in Canada were Canadian owned. If they were American owned you'll find the records in the USA.

Border Crossings
Name, Age, Date, Nationality, Occupation, Previous Residence, Destination; Sometimes included a name of a relative if they were sponsored.
Land
Homestead records vary in the information they provide. All have the name of the applicant and the land they settled upon. Some include information from the applicant regarding their reason for wanting the land, who was living with them, and where they came from.
Trains
Name, Place of Departure & Arrival, Date

If you have a scan of an Ontario Emigration Record, please consider sending it in to be included as an example.

Border Crossings
Library & Archives Canada: 1908-1935
Citizenship & Immigration Canada: 1936+ (Due to the Privacy Act these records are not accessible for public viewing)
U.S. National Archives: 1895-1954
LDS Family History Centres (worldwide): 1895-1954
Reasons For Emigration
Gold! Yukon Archives
Western Land: Library & Archives Canada (see their online homestead records database - linked below)
Trains: Archives of Ontario has some 'Emigrant Railway Pass Records' (link below)

Finding Ontario Emigration Records online is hit or miss. There isn't an organized effort to bring any of these records online. Emigration Records known by OntarioGenWeb to be online are linked below.

Citizenship/Naturalization Records (in the area they emigrated to)
Land Records (in the area they emigrated to)
Newspapers (both in Ontario and in the area they emigrated to)
Questions & Answers
Books
Links