A. I don’t know of any comprehensive prison indexes, though you can find a few records from individual institutions online. See Ancestor Hunt for a list. (I havent clicked all those linkssome may go to pay sites.)
Decennial US censuses typically enumerated prisons and other institutions (youll see the institutions name at the top of the return), so search for your ancestors name in censuses during his lifetime. Note that not everyone listed in censuses as inmate was in prisonpeople in orphanages and hospitals sometimes were called inmates.
You also could run searches of various online newspaper indexes to see if your grandfathers name turns up in crime-related coverage.
Do you know the places he lived? If so, you could always run place searches of the Family History Library catalog to see whether it has any microfilmed prison records from those counties or states, then rent the film through a Family History Center near you. Search state archives Web sites and catalogs, too, as state prison records would likely be with the archives.
But it sounds like youre taking a shot in the dark. Without a more-specific idea of when and where your grandfather may have served time, renting all that film will be time-consuming and expensive.
Aside from checking censuses and using the easily accessible online indexes mentioned above on the off chance you’ll find something, your best bet is to continue your general research of your great-grandfather and other relatives. Keep your eyes open for clues. Ask cousins whether they’ve heard anything about your grandfather being incarcerated.
For example, my family had a similar story about my great-grandfather, and only when I got his sons orphanage application (it mentioned the state penitentiary) did I learn when and where he was imprisoned, and where I needed to look for records.