Fort Delaware and Rockwood Mansion are not the only haunted places in Delaware, but they are two of the scariest locations. 

Sources:
https://destateparks.com/History/FortDelaware
https://www.haunted-places-to-go.com/haunted-prison-4.html
https://www.onlyinyourstate.com/delaware/ghosts-fort-delaware-de/
http://hauntedhouses.com/delaware/fort-delaware/
https://kellyskrazynews.blogspot.com/2009/06/haunted-fort-delaware-pea-patch-island.html