I find the data released by the US Treasury Department very interesting. These were the top ten countries holding US debt as of June 2007, according to a report released on April 30, 2008.
#1. Japan $1,197, 000,000,000 That’s 1.197 TRILLION dollars
#2 China $922 ,000,000,000 That’s 922 BILLION dollars
#3 UK $921,000,000,000
#4 Cayman Islands $740,000,000,000
#5 Luxembourg $703,000,000,000
#6 Canada $475,000,000,000
#7 Belgium $396,000,000,000
#8 Ireland $342,000,000,000
#9 Switzerland $329,000,000,000
#10 Netherlands $321,000,000,000
Oil Exporters came in #11, Russia at #17, and besides the Cayman Islands, there were also Bermuda at #13 ($238b) and the British Virgin Islands at #22($108b).
Source: Table 2. Foreign holdings of U.S. securities, by country and type of security, for the major investing countries into the U.S., as of June 30, 2007
https://www.treas.gov/press/releases/hp947.htm
My readings from the US press led me to believe that China was the prime holder. Now the information above may be out of date, but I have not read about our indebtedness to Japan. Or to the United Kingdom, or the Cayman Islands.