You can see several old maps online now via Geoportail
These are under Historie et Patrimoine
. There are a lot of different overlays of specific things (national monuments for example) as well as older maps; the Carte de Cassini
and the Carte de l'etat major
are the more interesting of these historically. The former doesn't show building detail but it's interesting to see if your hamo or village is there but the later does show individual buildings. You can overlay the maps to the current IGN ones and then vary the transparency to see them together - they line up pretty well (at least they do for my location) where I can see our hamo on both but our house and the road to it isn't shown even though it was built in the period of the map.
They also have three periods of overhead images so you can see how things are changing over recent years.