It appears that Foursquare hit the three million user mark sometime over the weekend. The location based social network has been adding users at impressive rates, and only hit 2 million users in early July. It took a year to reach one million; three months to hit 2 million, and a month and a half to hit 3 million.

Some thought Foursquare was doomed when Facebook rolled out its location-based feature, Places, a few weeks ago. In turns out that via the Places API, the feature serves as a platform for services like Foursquare and Gowalla. But Foursquare’s co-founder Dennis Crowley reported that Foursquare had its biggest day of signups following Facebook’s announcement. And Crowley told the LA Times recently that the startup is growing at about 180,000 users every 10 days.

To expand upon this growth Foursquare recently raised $20 million in funding at a $95 million pre-money valuation, led Andreessen Horowitz with existing investors Union Square Ventures and O’Reilly AlphaTech Ventures participating. The new funding is being used to hire additional staff, for product development and a new office space. And we know that Foursquare has some interesting ideas to incorporate gaming with check-ins. The company is also opening a San Francisco office.

While Foursquare appears to be growing faster than its main competitor Gowalla, other location-based social networks have already hit the 3 million mark. MyTown, another location-based network hit that number earlier this month, and Loopt passed 4 million users in July.

Of course, with massive billboards in Times Square are certainly going to help Foursquare possibly reach 4 million users in the next month. Plus, we hear a new version of the service will be unveiled soon.

Crunchbase

• FOURSQUARE

Company: Foursquare

Website: foursquare.com

Launch Date: March 11, 2009

Funding: $71.4M

Foursquare is a geographical location based social network that incorporates gaming elements. Users share their location with friends by “checking in” via a smartphone app or by text message. Points are awarded for checking in at various venues. Users can connect their Foursquare accounts to their Twitter and Facebook accounts, which can update when a check in is registered. By checking in a certain number of times, or in different locations, users can collect virtual badges. In addition, users...

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