In a Senate Intelligence Committee meeting hearing in March, Wyden asked "Does the NSA collect any type of data at all on millions or hundreds of millions of Americans?" Clapper replied "No, sir." When pressed by Wyden, Clapper elaborated that the NSA does "not wittingly" collect data about Americans, with the caveat that "there are cases where they could inadvertently perhaps collect" such information.
Of course, since then the Snowden revelations have shown that the NSA does, in fact, collect data on millions or hundreds of millions of Americans. At a minimum, we know that the NSA is collecting information about the phone calls of all Verizon customers, and it's a safe bet that the agency has similar arrangements with other major phone companies. That suggests the NSA likely collects information about everyone with a telephone, which is to say almost all of the approximately 300 million people in the United States.
Clapper denied that the NSA had collected information on "millions" of Americans, but he didn't actually say the number was zero. So we've given Clapper the benefit of the doubt, showing him as allowing for as many as 1,900,000 Americans being the subject of NSA data collection.
Clapper later apologized, calling his statements "clearly erroneous."