Bridgewater Bancshares, one of Minnesota’s fastest-growing banking companies, has received a $15 million investment from a California private equity firm that focuses on financial businesses.

Chief Executive Jerry Baack, a founder of the decade-old bank, said the money from Castle Creek Capital will be used to grow, including through possible acquisitions and to organically “continue expanding our footprint in the Twin Cities.”

“With this level of funding, we will be able to immediately meet the emerging financing needs of our increasing client base,” Baack said. “We have never had a difficult time raising capital, but an investment from Castle Creek elevates Bridgewater Bank to a new level.”

Baack called the investment “a true testimony to the quality of our franchise and a vote of confidence in our business model.” Bridgewater focuses on real estate and small-business entrepreneurs.

Castle Creek, north of San Diego, since 1992 has invested more than $2 billion in banks and other financial intermediaries, including acting as lead investor in 65 institutions. It is one of the nation’s most active investor-owners of small banks.

Privately held Bridgewater initially was capitalized in 2005 by Baack and other small-business people. Before the Castle Creek investment, Bridgewater had raised about $25 million in equity from 197 local investors.

Baack was a federal bank examiner and lender at other banks before starting Bridgewater.

Bridgewater, which caters to business owners and their companies, got through the recession and has grown rapidly and profitably during six years of economic recovery to become one of the 15 largest banks in Minnesota. It has assets of about $800 million.

The company had pretax earnings of $7.9 million during the first six months of 2015. Its loan portfolio grew 10.5 percent, or $62.8 million, during the same period.

Bloomington-based Bridgewater operates four offices, including downtown, and employs 70 people.