Allison Andresen, 26, foreground, and other employees at OPower in Arlington on May 16, 2014. (Dayna Smith for the Washington Post)

OPower, a fast-growing Arlington-based green technology company that was being aggressively wooed by the District and Maryland, will stay in Virginia, Gov. Terry McAuliffe announced Tuesday from the company’s offices.

The firm, which creates cloud-based software for the utility industry, employs 329 mostly millennial-age workers in Virginia, and expects to add 70 more in the coming three years. The seven-year-old firm has 595 full-time employees worldwide.

McAuliffe (D) approved a $1 million grant from the Commonwealth’s Opportunity Fund to help the company defray the $10.45 million cost of leasing a new company headquarters at 2311 Wilson Blvd. Arlington County will match the state funding with an annual performance grant, starting this year and through 2018, dependent upon OPower’s promise of new hires and its occupying 63,000 square feet in its new building. The county, will offer an additional performance-based grant for each of the seven years after that.

Virginia’s Jobs Investment Program will also provide $140,000 to support the company’s employee training activities.

The Arlington grant is the first time the county has ever made a grant to recruit or retain employers.