As discussed in the RYPN discussion thread Doug linked to, there was at least one swinging pontoon railroad bridge in the northeast US as well, this on the Rutland RR at Larrabee's Point on Lake Champlain, connecting Shoreham, VT with Ticonderoga, NY (and interchange with the D&H). It was dismantled after World War I.
(The Rutland seems to have had a weird fixation with crossing Lake Champlain, as they also had a more conventional pile trestle crossing between Alburgh, VT and Rouses Point, NY, again connecting with the D&H; the remains of the Rouses Point trestle are still easily visible in Google satellite views.)
-Philip Marshall