Upper Canada Land Petitions are the actual Petitions for land which were submitted in Upper Canada (Ontario).
Here is an actual 1797 UCLP (Upper Canada Land Petition) for one of my ancestors. In the petition, the petitioner gives his father's name, the date he (and his father) arrived in Upper Canada (Ontario) and specifics of his family (wife and children). He requests land, and the outside of the folded petition reveals if that request was granted (a land grant) and under what terms.
These land petitions frequently contain information about the petitioner and his or her family. Loyalists and discharged soldiers often mentioned the regiment in which they served. To find an ancestor you must first consult an index, then convert your findings to a microfilm reel with the full petitions. See Upper Canada Land Petition for more help with this important genealogical research tool.
You should also consult Finding a Loyalist Ancestor for help if you have a Loyalist or two in your tree
I have already discussed CLRI (Ontario Land Record Index) and will be explaining other land records such as Township Papers, Land Books etc in future Blog Posts.