I discovered this institution yesterday. It's called: Mississippi State Insane Asylum, located at Whitfield, MS 15 mi. outside of Jackson, MS. History indicates that the institution opened prior to the start of the Civil War - possibly as early as 1848 - (but don't quote me). In 1920, the census was abt. 1,600 - by 1935 there were over 2,500 patients and the site was moved elsewhere - "Rankin Farms", a former prison property. ALL such records are PRIVATE and are controlled by the State. If your relative was housed at the institution on a census year, you may be able to find the person that way - eg. 1870, 1880, or 1900 census. Mississippi State Asylum has no cemetery - the burials are apparently in unmarked graves. I wish you well!