The spacs for rs-232 say 50', but people have successfully used cable runs of a couple hundred feet. A lot of it depends on the speed, and the cable used.

If you need longer distances, try finding some line drivers that convert to/from rs422 or rs485, BlackBox is a well known source. Specs typically claim 115.2 up to 4kft.

BTW: it's a DE-9 (the second letter indicates the physical connector shell size.)