Foursquare is celebrating its third-annual 4sqDay in impressive fashion.

Whenever users check in on the service today, they'll be awarded the 2012 4sqDay badge, which is accompanied with a message announcing that the startup now has 20 million users worldwide, and has hit a whopping 2 billion check-ins since it was founded in 2009.

"In 2010, Foursquare fans declared April 16 4sqDay (4/4^2 - nerds after our own heart!)," the message that accompanies the badge reads. "Two years and two billion check-ins later, you're still why we get out of bed each day. Thanks to all 20 million of you for making us part of your lives. Happy 4sqDay!"

Foursquare's growth appears to be accelerating. Back in June, the company announced that it had reached 10 million users after two years. In less than a year, it has added another 10 million users.

Foursquare's success to this point has not gone unnoticed. Just about every major company is getting in on the location-based services market, including Facebook, which lets users say where they are from the company's mobile app.

Still, through it all, Foursquare continues to grow.

Investors have taken notice of that growth. Just after Foursquare announced that it had hit 10 million registered users, the company secured $50 million in a financing round led by venture-capital firm Andreessen Horowitz. O'Reilly AlphaTech Ventures and Union Square Ventures also participated in the round.

(Via The Next Web)