Specifically, the relative I sought was William Winsor, my 3rd great-grandfather. He last appeared in the 1860 census in Duxbury, Plymouth County, Massachusetts, and that was that. I thought I had a brick wall until a Google search revealed a man of the same name was a lighthouse keeper at Tatoosh Island in Washington state.
More research revealed he had migrated west with other men from Duxbury - Rufus Holmes and Alexander Sampson. After the initial Google searches gave me more information and a few mentions in books, I went to the Rootsweb message boards for Clallam County in Washington State and posted a query.
The responses from another member yielded some interesting results, including diaries and personal letters, both available from the University of Washington Library and Special Collections.
So it's always worth investigating local colleges and universities to see if their libraries offer more than you expected, such as special collections or manuscripts. A good place to start is their website to see what they have. They may even offer a searchable index of materials and/or people and places mentioned in such materials. That is how the Rootsweb user who found links for me managed to find my great-great-great grandfather in the University of Washington's collections.
If you're looking for collections including personal documents, reach out to the university in the area where your ancestor lived and worked. You might be pleasantly surprised.
Copyright (c) 2015 Wendy L. Callahan