1. The biggest holder of US government debt is the United States itself. The Federal Reserve system of banks and other US intergovernmental holdings account for a stunning $4.806 trillion in US Treasury debt. And with recent announcements from the Fed, potentially another $1 trillion may be added to its balance sheet... About a decade ago, the total government holdings were "only" $2.5 trillion.

2. According to the Federal Reserve, mutual funds hold the second largest amount of US debt compared to any other group. Including money market funds, mutual funds and closed-end funds, this group of investments manages approximately $769.1 billion of US Treasury securities.

3. The buzz word in the market for US debt of recent has been China. The world’s most populous country is also the largest and most important international buyer of US debt. From September 2008 to January 2009, China raised its stake by over $120 billion. Standing at $739.6 billion in January, China’s holdings have skyrocketed from $492.6 billion from a year earlier. Hong Kong, which is not included in China's total, holds an additional $71.7 billion.

4. Another major US trade partner, Japan holds a huge amount of the country’s debt, with a stunning $634.8 billion. As recently as January 2008, Japan held the more US debt than any other country, but currently holds the #2 spot, as far as foreign governments are concerned.

5. US state and local governments have over a half-trillion dollars invested in American debt, according to the Federal Reserve. The level of investment has remained very stable over the past three years, moving within the range of $516.9 billion and $550.3 billion from 2006 to 2009.

6. Pension funds control large amounts of money, reserved for personal retirements, and thus are obligated to make relatively safe investments. This group includes both private and local government pension funds, totaling $456.4 billion. The private pension fund category also includes US Treasury securities held by the Federal Employees Retirement System Thrift Savings Plan "G Fund."

7. Although the most recent numbers for this category are from September 2008, this extremely diverse group includes individuals, government-sponsored enterprises, brokers and dealers, bank personal trusts, estates, corporate and non-corporate businesses for a total of $413.2 billion.

8. Big oil means big money... and big investment into US debt. Included in the group of oil exporters are Ecuador, Venezuela, Indonesia, Bahrain, Iran, Iraq, Kuwait, Oman, Qatar, Saudi Arabia, the United Arab Emirates, Algeria, Gabon, Libya, and Nigeria. The group combines for a total of $186.3 billion, up from $140.8 billion one year earlier.

9. The US Treasury identifies this group as institutions in the Bahamas, Bermuda, the Cayman Islands, Netherlands Antilles, Panama and the British Virgin Islands. Holdings recently hit $176.6 billion, up from $109.2 billion in January 2008.

10. The South American economic giant has $133.5 billion in holdings, according to the Treasury. Brazil’s holdings of US debt have been relatively stable over the past year, with a high of $158 billion in June, and a low of $127 billion in December.

11. According to the Federal Reserve Board of Governors, insurance companies hold $126.4 billion in Treasury securities. This group includes property-casualty and life insurance firms.

12. Britain currently holds $124.2 billion in US debt, but the number has fluctuated dramatically in the past year, ranging from $279 billion, but dropped to as little as $55 billion in the summer of 2008.

13. Russia's investment in US debt has grown over 330 percent in the past 12 months, from $35.2 billion in January 2008 to $119.6 billion in January 2009.

14. As of the fourth quarter of 2008, the Federal Reserve Board of Governors lists depository institutions as holding approximately $107.3 billion in US debt. This group includes commercial banks, savings banks and credit unions.

15. A country slightly smaller than Rhode Island currently holds $87.2 billion in US government debt. Over the past 12 months, Luxembourg’s holdings have ranged between $66.1 billion and  $104.7 billion.