The Leeds-Grenville Genealogical Society recently shared this information, which we thought to pass on here:
We certainly have some information on early militias in the area, including a copy of the book, Soldiers of the King. We also have a publication entitled Land Claims Certificates of Men Who Fought in the War of 1812, as well as copies of early census records for Leeds and Grenville (or as it was at the time Eastern District and then Johnstown District) and some records compiled years ago by a Joel Stone and found in our Livingston Collection of documents.
The Archives of the Leeds & Grenville Branch of the Ontario Genealogical Society is located in the basement of the Brockville Museum at 5 Henry Street. Our hours of operation in the winter are Monday-Friday from 1-4, when we have a researcher on hand to help locate information.