Cohan's songs could be considered American "folk songs" now, since they were all (at least all the ones I can think of at the moment) written before 1922 and are PD, not to mention, in the case of "Over There," "Grand Old Flag," and "The Yankee Doodle Boy," very familiar to folks in the US.  Katherine Lee Bates's and Samuel Butler's "America The Beautiful" and,of course, "America," are also PD. Come to think of it, most of the really well known "American patriotic songs" are PD by now.  But Irving Berlin's "God Bless America," Woody Guthrie's "This Land Is Your Land," the Weavers' "Wasn't That A Time," and Lee Greenwood's "God Bless The USA" are not and won't be for a long time.  (Berlin "gave" "God Bless America" to the Boy Scouts, so royalties go to them, rather than to Berlin's heirs.)  One really pretty one with not-so-jingoistic lyrics is "The House I Live In," which was written by Millard Lampbell and Earl Robinson during WWII, is also still copyright protected.

Many people have tried and are still trying to write what will become American patriotic standards, but I think the current copyright laws work against that happening.  You can't even hand out song sheets for them at a picnic without being in violation of copyright laws.
 

Genie