The 1921 Census of Canada was released in 2013 and is available free of charge on Ancestry.ca, whether or not they have a paid Ancestry subscription membership.
No alphabetical index exists, so you cannot (yet) search for a person by name. However, you can browse the census pages by district and subdistrict. Note that the City of Kingston is treated as a separate district--it is not a subdistrict of Frontenac County.
Access to the Ancestry Library Edition website is restricted to KFPL branches. A subscription is required outside of the KFPL network.
Find your Ancestors in the 1921 Canadian Census. Canada added 1,581,840 new residents between 1911 and 1921. The Prairie Provinces were the big gainers, with Alberta and Saskatchewan each growing by more than 50 percent.