Historical Indiana Plat Maps
Plat maps are wonderful, not only to jump-start the process by narrowing down when your ancestor owned the land, but to see at a glance who your ancestor's neighbors were (which is especially helpful when doing collateral research).
Due to their large size and often fragile condition, historical plat maps for Indiana are not likely to have been digitized, so as a general rule you must visit local libraries and archives to view them. However, here are some notable exceptions.
Visit Indiana Genealogical Society Blog for more information.