Top ten American composers/songwriters

Tod Rundgren
Greg Allman
Paul Simon
Alan Hovhaness
Joni Mitchell
Ferde Grofé
J.P. Sousa
Woody Guthrie
Huddie Ledbetter
Louis Armstrong

Keep ’em coming. A lot of quality names. Leonard Cohen, however, is a Canadian. Ahem...  But Joni can be counted in because she abandoned Canada for New York and then L.A.

Foster, as in David Foster......he’s a Canadian also.  Perhaps the OP meant North American

A lot of the greats already listed. I’ll add Brian Wilson, Chuck Berry, Dave Bartholomew, Pomus/Shuman, Leiber/Stoller, Willie Dixon, Buddy Holly, Hank Williams, Merle Haggard, Randy Newman, Jackson Browne, Iris Dement, John Hiatt, Rodney Crowell, Felice & Boudleaux Bryant, Goffin/King, Greenwich/Barry, Mann/Weil, and Holland/Dozier/Holland (writers of the sublime "What Becomes Of The Broken Hearted").

Robert Ellsworth Pollard at the top of the list.