Facebook said Tuesday morning it will boost its already-sizable Prineville campus by more than 80 percent.

The company said it will add nearly 1 million square feet of data center facilities by 2021. It will start building its fourth data center at the site this month. Work on the fifth building is expected to start next year.

The fourth building is set to be completed in 2020 while the fifth is on track to open in 2021. The new structures will add 900,000 square feet to the 1.25 million-square-foot campus. Facebook is also adding a 70,000-square-foot administrative space that connects the two buildings.

The social media company didn't give an exact cost but said it represents hundreds of millions. Facebook said the existing data center, which employs 200-plus workers, represents a $1 billion-plus investment.

Facebook plans to add two new buildings  to its Prineville data center by 2021. (Facebook)

"This translates into keeping construction crews busy for another four years, plus additional full-time jobs as the data halls come online," the company wrote.

Facebook has pledged to work with clean energy sources as much as possible in Prineville. In October, it called on the state to open more such power options for its data centers and others

Photos: Inside the Facebook data center in Prineville.