If you need any further evidence that the mobile payments arena is going to be huge over the next few years, just look at Square.

The mobile payments startup, created by Twitter founder Jack Dorsey, has raised $100 million in a third round of funding led by Kleiner Perkins Caufield & Byers, skyrocketing the company’s valuation to more than $1 billion, the Wall Street Journal reports.

The funding has quadrupled Square’s valuation — the company’s last round valued it at just $240 million. That’s an impressive jump for any company, let alone one that’s just eight months old. The funding shows that investors are confident Square can hold its own against the likes of PayPal and Intuit, who are more established when it comes to payments but are just now beginning to take mobile transactions seriously. And of course, Google’s recently launched mobile wallet could pose a threat as well.

As if there isn’t enough good news for Square, Kleiner Perkins partner Mary Meeker will join the company’s board. “We’re making a bet that Square has the right product at the right time,” she told the WSJ.

Square allows anyone to make credit card transactions on their mobile devices. The company offers free card readers that plug into your phone or tablet’s headphone jack, and it takes a 2.75 percent cut from every transaction. Signatures occur right on the device using your fingertip, and the transaction receipt gets emailed to you afterwards.

The technology was initially conceived of as a way for artists and flea market vendors to easily accept credit cards, but it could just as easily serve as a complete register for a small business with the recently released Register iPad app. Square also recently released Card Case, an app that allows consumers to automatically pay for purchases from stores without swiping any cards.

Chief operating officer Keith Rabois says the company is processing nearly $4 million in payments every day, and it expects to surpass $1 billion by year’s end. Thinking strategically, Dorsey has also added heavyweights to Square’s board, including Sun Microsystems co-founder Vinod Khosla and former Obama chief economic adviser Larry Summers.

With its most recent round, Square’s funding now totals $137.5 million. Kleiner Perkins is just the latest in a bevy of powerful investors in the company — its last two rounds were led by Sequioa Capital and Kohsla Ventures.

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