The $50 million Big Otter Wind Energy Project would be built on 3,500 acres of private land about 20 miles from Great Falls, the Associated Press said.
Invenergy said it has another 40,000 acres for future phases of the project.
The company has not yet secured a power purchase agreement for the project. It asked for an 18-month window to begin construction after receiving the permit, rather than the usual six months.
Invenergy already operates the 135MW Judith Gap Wind Farm in Wheatland County, Montana. It was completed in 2005, uses 90 GE 1.5MW turbines.
Invenergy has reserved 350MW on the planned Green Line transmission project, to export electricity from two Montana wind farms to the Pacific Northwest.