Sometimes they avoided the census. In my case my gr-grandfather's name was spelled totally wrong - they combined his first and last names into one surname. The only way I found him was by knowing some of his neighbors names (they were related) and locating them first. I use Automated Genealogy to look at the index first and then link to the actual census. He may also have been away from home at the time of the census. I know of one family back in those days who lived in a very unaccessable place so the census taker either didn't know they were there or couldn't get to their place.
Good luck .