To add my 2 cents,  I also have found this type of doorknob here in
Wisconsin and also in Kentucky. I think that it is likely to be found
nationwide. Both sites fit the temporal context of the doorknobs.

Andrew R. Sewell, M.S., RPA
Historic Archaeologist
ORISE Program Participant
Fort McCoy Archaeology Laboratory
Building 104
Ft.  McCoy Wisconsin 54656
phone: (608)-388-8257
fax: (608)-388-3319

"Whosoever diggeth a pit, must lay in it."
                                        -Bob Marley, "Small Ax"