I am looking to get some statistical data that shows the percentage of
American's considered to have "poor credit."  Poor credit can either
just be called poor credit or it can be listed as credit scores below
580.

"The median FICO score is 723. The national distribution of FICO score
statistics are as follows:
Up to 499 ? 2% 
500 to 549 ? 5% 
550 to 599 ? 8% 
600 to 649 ? 12% 
650 to 699 ? 15% 
700 to 749 ? 18% 
750 to 799 ? 27% 
800+ ? 13%"
http://www.poorcreditgenie.com/solutions.html

If you add the first 2 percentages (2% + 5%) and half of the third
(1/2 * 8%) then you see that about 11% of the population has a FICO
score below 580.

Do keep in mind that there are several other credit scores besides
FICO (ScoreX, VantageScore...), and there are 3 different credit
reporting agencies (TransUnion, Experian, Equifax) that each have
different information about you.  So each credit agency will have a
different FICO score for you, and there are other scores that many
lenders consider other than FICO.