Short answer: we borrowed 40% of it! About a quarter of 2009 government receipts came from individual income taxes, about a quarter of it came from payroll taxes, 4% came from corporate income taxes, and the remainder from excise and miscellaneous taxes.
Where did it go?
Note: the 5% in net interest payments is likely to go up a lot in the future. Interest rates on US government debt have been minuscule in recent years, a situation unlikely to persist indefinitely.