Have you actually gone over the micro films visually or did you do an electronic search on a data base? If the latter, then you need to consider that variations in spelling and name variations make a big difference. As an example, I searched in several data bases for many variations on Henry Munford Johnston in Fresno, CA in the 1900 census; to no avail. I finally found him as Harry Johnson; but only after hours of looking over the many pages of micro film. I had even done a search on that variation, but it did not come up. Not only did my relative use a "nickname" but the census taker also left a letter "t" out of the surname. An Anglo-Saxon census taken might very well have mis-spelled an Italian name he was not familiar with. Search engines are great, but they do not always work. Alas, Memphis in 1900 has many people to look through. Another possibilty, could your family have been in West Memphis in Arkansas, or perhaps in some other town nearby, but not in Shelby Co.?