Not only Americans are getting dumber. In Europe the same process started also. Mainly evoked by brainwashing media like tv.
About seven years ago somebody wrote on the Internet: "there will come a time where humanty will be split in on-liners and off-liners.
The on-liners will have all the knowledge, the off-liners non.
I think it's already happening.

I've come across some pretty dumb on-liners, myself included.

Oh, don't blame the media. TVs have an OFF button, and so do remote controls; it's us that don't push them.

The illiterate of the 21st century will not be those who cannot read and write, but those who cannot learn, unlearn, and relearn.
Alvin Toffler

pop for the Toffler quote

I just saw on Bill Moyers' PBS show, one of the best on TV, that only 16% of high school and 23% of college students could find Iraq, Iran, Israel or Afghanistan on a map. Duuuh...!