In a move that makes it the largest commercial landlord in Sonoma County, Basin Street Properties announced a $70 million deal Wednesday to buy 17 Santa Rosa office buildings.

"We're thrilled," said Matt White, president of Basin Street. "We know most of the customers in Sonoma County, and we've been working in the county for 38 years. So we could not be happier to be back in Santa Rosa."

Basin Street previously owned 14 of the 17 properties and managed the remaining three buildings. They were part of a group of properties that Basin Street sold in 2005 to Equity Office Properties for $263 million, one of the largest commercial real estate transactions in Sonoma County history.

Basin Street bought the Santa Rosa buildings back for 50 cents on the dollar, White said. The deal closed last week, he said.

"When we put the portfolio together originally, it allowed us to serve all the various customers in the market, so the portfolio coming back to market was very attractive," White said. "When you factor in that we bought it for about 50 cents on the dollar for what we sold it, the numbers were very compelling."

The company, which moved its headquarters from Petaluma to Reno, Nev., in 2009, is now the largest commercial real estate owner in Sonoma County, with nearly 2 million square feet.

The portfolio of buildings it reacquired last week spans 697,500 square feet at six locations. Tenants in the buildings include Kaiser Foundation Hospital, Medtronic, Summit Engineering, Sonoma National Bank, Moss Adams and the County of Sonoma.

Basin Street plans to invest millions of dollars in facility upgrades and tenant space improvements.

The company has bought 25 buildings in Sonoma County since last year, including eight buildings in the Redwood Business Park in Petaluma. All but three of the 25 properties were part of the sale to Equity Office Properties.

Basin Street has now reacquired 75 percent of the local buildings it sold to Equity Office, the company said.

"I would say that's a very strong testament to the strength of our economy going forward," said Al Coppin, president of Keegan & Coppin, a commercial real estate firm. "They're a very good landlord and a very responsible, community-minded company, so it's great to have them back."

The Santa Rosa buildings purchased by Basin Street are now about 75 percent leased, White said. The company employs 30 people in Sonoma County, and plans to hire another six thanks to the deal.

The local commercial real estate market is recovering, trailing the markets in San Francisco and Silicon Valley by about 18 months, White said.

"We're ecstatic," said Scott Stranzl, vice president of leasing for Basin Street. "We feel that the market and the opportunities in Sonoma County are moving forward and we're thrilled to be a part of it."