Did you know that there are books about prisoners and you can even find them digitized online sometimes? I found a book in the familysearch.org catalog about Georgia prisoners who were listed on the 1880 census. The full title of the book is “List of prisoners in penitentiary, convict camps, chain gangs and jails in Georgia : including a list of guards, jailers, sheriffs and others, from 1880 federal census records“.
You can view this book online through this link. https://familysearch.org/search/catalog/1452769?availability=Family%20History%20Library
If you find an ancestor who was in prison on a census, try finding a book by going to FamilySearch.org, click on the Search tab, then the Catalog tab and then do a place name search for the state where your ancestor lived. You can also search on the county level as well.
Let me know if you find anything interesting and if you have any questions.