The company had signed a temporary agreement in January to buy the property for a little more than $1 million. Microsoft officials finalized the deal Thursday.

"We are excited," said Curt Morris, board president for the Port of Quincy, which owns the industrial park. "I never had any doubts, but in the real estate world, things can always go haywire."

The Redmond-based company hasn't released many details about the project. Documents filed with the city show plans for as many as six buildings, totaling nearly 1.5 million square feet, that would house racks of computers to store data. The plans include an electrical substation, as well as a diesel-powered generator that would provide backup power.

Construction is expected to begin this month. Microsoft already is looking for area apartments to house workers during construction and setup, Morris said.

Internet giant Yahoo Inc. also has signed a tentative agreement to purchase 50 acres in a nearby industrial park. The company, based in Sunnyvale, Calif., has until the end of April to seal the deal. The company also has signed a 10-year, roughly $6 million lease to set up a separate data center in Wenatchee, about 30 miles away.

The projects come as Microsoft, Yahoo and Google Inc. are boosting the amount of data such as e-mails they'll offer to hold for people, part of efforts to compete for customer loyalty.