The number of U.S. fatalities in Afghanistan is nearing the 1,000 milestone as well, highlighting a steady trend of climbing fatalities in the effort, as the U.S. has sent more troops to take on al Qaeda and Taliban strongholds in that country.
While the death toll in Afghanistan climbs, U.S. losses in Iraq have gone down.
At least 312 U.S. soldiers died in Afghanistan last year, nearly twice as many as in 2008. In Iraq, 150 Americans lost their lives, half as many as the year before.
December 2009 was also the first month without a U.S. combat death in Iraq since the U.S.-led war there began in March 2003.
4,371 military service members and 13 department civilians have been killed in Operation Iraqi Freedom, according to Pentagon reports.
Military officials and analysts predict the trend will continue into 2010 as the U.S. continues to draw down forces in Iraq and build up troop levels in Afghanistan as part of President Obama's new military strategy there.
They have also warned that the number of U.S. casualties in Afghanistan will likely rise in the short term while forces carry out the new mission.
About 72,000 U.S. troops serve in Afghanistan with 30,000 more expected to arrive by late this year to help fight Taliban insurgents and enhance security for Afghan civilians. By the end of 2010, roughly 100,000 U.S. troops will be stationed in the region.
Defense Secretary Robert Gates, in an interview with ABC News Dec. 2, said Americans should expect more casualties in 2010.
"Every life is precious," Gates said. "We lost 15 soldiers and Marines in November. We lost 44 in October. Casualties will vary as we go into the winter, but come spring, those casualties will grow."
But several military experts said the rise in casualties will likely only be temporary as the surge takes effect.
Retired Army general and ABC News military consultant William Nash said, "There will be more targets, but there will also be more security, which will ultimately decrease casualties.
"The key is going to be synergy between military, politics and economics," he said, adding that prospects are not favorable in the short term. "But over a period of one or two years, I think there's a great opportunity to make progress."