I could not find Rockport on the original Nebraska land surveys for the area done about 1856. and the town seems to have been more or less abandoned by 1882. I found on reference to Rocksport (washington co) in the Nebraska History Magazine Vol. 59 page 621. I gave my copies back to the Society when I left Nebraska so you will have to look up the reference to see what it says. Rockport was so small and of such short duration it did not get mentioned in Nebraska Place Names.
That looks like all the help I can be