foursquare-day It’s 4/16 and for fans of the social network application Foursquare, it’s cause for celebration. All across the world, Foursquare users are celebrating Foursquare Day by gathering in swarms and taking advantage of Foursquare deals offered by bars, restaurants and other venues. The big day could also potentially be the day Foursquare reaches one million members.

According to Co-Founder Dennis Crowley, who joined me on NBC San Diego earlier this morning (see video below), the company had nothing to do with the day except the creation of a special badge — it was devised 100% by fans of the service.

It all started in Tampa, where optometrist Nate Bonilla-Warford decided that since four squared equals 16, 4/16 should be known as Foursquare Day. With just a few weeks of lead time, Foursquare’s passionate user base has managed to turn the day into a global social media festival that will be celebrated at more than 150 swarms (a.k.a parties).

Foursquare’s having its own official party in New York City at The Hotel on Rivington, but you can check out the hundreds of other parties and events scheduled — it’s not too late to add your own — on the Foursquare Day website.

Crowley also noted that Foursquare is fast approaching one million members; last time we checked it had about 725,000 users and 22 million checkins. In a follow up conversation, Crowley said that Foursquare is about 80,000 shy of the one million mark and that it normally adds 10,000 to 20,000 new members a day. We have a feeling that today will be a landmark day for the startup, but is it enough to get them to one million on Foursquare Day? We can only wait and see.