It looks like 2009 closes out with the lowest possible number there can be for US soldier hostile-fire fatalities in a month: The big ZERO!
There were 4 non-hostile fire US soldier fatalities in Iraq this December, so December 2009 will go down as the new record low for US soldier fatalities in a month.
The last Iraq War US soldier hostile-fire fatality came on November 22nd, which is obviously a record span of time between incidents. The last Iraq War US soldier non-hostile fire fatality came on December 11th and this also sets a new record span of time in the Iraq War without a US soldier fatality.
For the year there were 75 US soldier hostile-fire fatalities and 75 US soldier non-hostile fire fatalities making this the least deadly year of the conflict.
Update: It turns out there were 74 US soldier hostile-fire fatalities, not 75.