The number of people holding security clearances rose to about 4.9m in 2012, according to the latest official figures (pdf) from the Office of the Director of National Intelligence (ODNI).
Steven Aftergood of the FAS Security blog provides more details:
The total number of cleared personnel as of October 1, 2012 was 4,917,751. Although the number of contractors who held a clearance declined in 2012, the number of eligible government employees grew at a faster rate, yielding a net increase of 54,199 clearances, or 1.1 percent, from the year before.
It is possible that there were more security-cleared Americans at some points during the Cold War, when there was a larger standing military with more cleared military personnel than there are today. But until 2010, no comprehensive account of the size of the security clearance system had ever been produced. So the new 4.9 million figure is the largest official figure ever published.
As he notes, ODNI requested that the legal obligation to report these numbers be canceled, which was initially granted, but following a public outcry, the obligation was restored (ODNI claimed it took a lot of time and effort to prepare).
It’s very useful for us to know these numbers, and indeed further information could well be disclosed without threat to national security, such as the number of contractors working at each IC agency, and in what capacity.