The table on this page will link you to a Social security Death Index of anyone who listed Lewis County as their last place of residence. It is arranged by death years. It is by no means a complete listing of those who died in Lewis County, but it will give the researcher a starting place to look. Each entry will list the person's name, birth date, death date, and social security number. Knowing where the Social Security number was issued may tell you of migration patterns for that individual. Good luck with your research.
A very good tutorial on using the Social Security Death Indices is located on the Rootsweb site and can be found at http://www.rootsweb.com/~rwguide/lesson10.htm#numbers .