Facebook accounts for nearly one out of every three online display advertisements in the U.S.
And that share makes Facebook the leading player in the online display market as measured by comScore AdMetrix.

The research company tallied almost 1.11 trillion display ad impressions in the U.S. during the first three months of 2011, and Facebook had 346 billion of them, or 31.2 percent.

The social network had only 16.2 percent market share in 2010′s first quarter. You could call that a rise of 15 percentage points but it’s really a doubling of market share.

Plus the overall market for online display ads has grown too, which makes Facebook’s growth all the more impressive. Like Jeff Hackett, comScore executive vice president, says in a press release:

The U.S. online display advertising market maintained its strong momentum from last year with a terrific first quarter. We are now seeing more than one trillion display ads delivered every single quarter and nearly 300 individual advertisers spending at least $1 million a quarter on display, numbers which underscore just how large and vibrant the online medium has become. And it’s not just about the volume but about the quality of the advertising experience that can be delivered as we see continued investment in compelling, high-quality creative that helps cultivate long-term brand equity.

Now that Facebook dominates online display ads in the U.S., the next likely objective for the social network is further expansion overseas — in addition to maintaining or growing its market share domestically.

What do you think about the latest quarterly numbers from comScore?