Global forests capture and store significant amounts of CO2 through photosynthesis. When carbon is removed from forests through harvest, a portion of the harvested carbon is stored in wood products, often for many decades. The United States Forest Service (USFS) and other agencies are interested in accurately accounting for carbon flux associated with harvested wood products (HWP) to meet greenhouse gas monitoring commitments and climate change adaptation and mitigation objectives. National-level forest carbon accounting has been in place for over a decade, but there is an increasing need for accounting at the scale of smaller administrative units, including USFS Regions and individual national forests. This paper uses the Intergovernmental Panel on Climate Change (IPCC) production accounting approach and the California Forest Project Protocol (CFPP) to estimate HWP carbon storage from 1906 to 2010 for the USFS Northern Region and its eleven national forests, which span northern Idaho, Montana, South Dakota, and eastern Washington. For the Northern Region as a whole, carbon stocks in the HWP pool were increasing at one million megagrams of carbon (MgC) per year in the mid-1960s, with peak cumulative storage of 28 million MgC occurring in 1995. Net positive flux into the HWP pool over this period is primarily attributable to high harvest levels in the middle of the twentieth century. Harvest levels declined after 1970, resulting in less carbon entering the HWP pool. Since 1995, emissions from HWP at solid waste disposal sites have exceeded additions from harvesting, resulting in a decline in the total amount of carbon stored in the HWP pool. The Northern Region HWP pool is now in a period of negative net annual stock change because the decay of products harvested between 1906 and 2010 exceeds additions of carbon to the HWP pool through harvest. Though most individual national forests mirror Regional-level trends in harvest and carbon flux, the timing and magnitude of change differs among forests with some forests departing notably from Regional trends. Together with estimates of ecosystem carbon, Regional and Forest-level estimates of HWP carbon flux can be used to inform management decisions and guide climate change adaptation and mitigation efforts by the agency. Though our emphasis is on national forests in the Northern Region, we provide a framework by which these accounting methods can be applied more broadly at sub-national scales to other regions, land management units, and firms.