American Poultry Association. There is also the American Bantam Association (ABA)
They don't recognize many of the modern hybrids such as what are in my area called black sex-links (Black Stars) golden sex-links (Bovan Browns), red sex-links (Red Stars), and Easter Eggers (often abbreviated to EE).
A breed has to undergo years of breeding, along with having a written out standard, and a bunch of other qualifications to be admitted into the APA. Just because it is not in the APA does not mean it is an "American" bird, it just hasn't been bred to a standard.