Series consists primarily of correspondence from members of W.L.M. King's family. The files contain letters, telegrams, and a sampling of clippings. The letters are arranged chronologically up to the end of 1917. Correspondence after this point is usually filed alphabetically by name of correspondent. The letters of his parents, Mr. & Mrs. John King, his brother, Dr. MacDougall King, and his sister, Mrs. H.M. Lay, are significant components of the collection. Special documents in this series include wills and papers relating to the disposition of estates of close relatives. Included with the family papers are photostat copies of letters and documents of W.L.M. King's famous grandfather, William Lyon Mackenzie (journalist, politician and leader of the 1837 armed revolt in Upper Canada). One of the oldest documents in this collection is a petition produced by Mackenzie in 1833 when he was a member of the Legislative Assembly. Other files which have been placed at the end of the series include the subjects: Mackenzie House, Woodside, (Volume 24), Niagara Falls and Queenston Ceremonies, 1938 (Volumes 24-25), Mount Pleasant Cemetery (Volume 25) and Genealogy (Volumes 25-26) as well as a number of files on King's dogs, Pat I, Pat II and Pat III (Volume 26).
Oversize items have been removed and placed in four oversize boxes at the end of the series (Volumes 28-31). Newspaper clippings have been removed and replaced with xerox copies.