FORTUNE — Etsy, an online shopping site that has over 40 million members who sell everything from homemade crafts to clothing, signed a 200,000-square-foot lease on Monday. The space, which is located at the foot of the Manhattan and Brooklyn bridges in Brooklyn’s Dumbo neighborhood, was a former Jehovah’s Witnesses property.

The deal, meanwhile, has brokers and developers optimistic that Brooklyn can become a place tech companies come to set-up offices in the future. The hope: one day replace Manhattan for the top tech spot in the city. Or at least give the borough some future stiff competition from less mainstream companies.

“We were so committed to Brooklyn that we looked under every rock. We talked to everyone. We did not look in Manhattan at all,” said Chad Dickerson, Etsy’s chief executive. The company was founded in 2005 in a Fort Greene apartment. Its last office space was 15,000 feet.

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New York State reportedly helped in Etsy’s decision to grow in Brooklyn by offering $5 million in tax breaks. As a result, Etsy has promised to add to its number of employers in its Dumbo and Hudson Valley offices to 740 from 400 currently.

In an interview with the Wall Street Journal, Kenneth Adams, the president and chief executive of Empire State Development, said, “In our discussions with Etsy, it became really clear that they’ve got locations around the country and the proposed expansion, which is close to 400 new jobs, was so significant that it was very important to us to capture all of the expansion in New York state.”

Etsy’s Dickerson said, “Etsy was founded in New York, and we’re excited to commit to our future here. New York is where creativity and commerce come together. It couldn’t be a more natural home for Etsy and for the burgeoning technology industry.”

Etsy’s lease is one of Brooklyn’s largest in the last 10 years.