The deal is for Siemens 2.3MW turbine, which will be installed across five different projects.
In April, MidAmerican was given the green light for the development of 1.05GW of wind power in the Midwestern state by the end of 2015.
The projects are the 500MW Highland Wind project in O'Brien county, the 250MW Lundgren plant in Webster county, the 138.6MW wind farm in Grundy county, the 117MW Macksburg project in Madison county and a 44.6MW expansion to the Vienna wind farm in Marshall county.
Windpower Monthly reported in May that Siemens were tipped to win the deal. A statement from the company had been included in MidAmerican's regulatory filing for the project, along with one from GE.
The blades for the turbines will be manufactured at Siemens' Fort Madison, Iowa, facility, while the nacelles will be made at Siemens' Kansas factory.
Facebook is expected to buy some of the power generated by the wind farms, with the social media group looking to sign a power purchase agreement to provide energy for its new $300 million data centre in Altoona, Iowa.
All of the sites have been bought from previous developers at a pre-construction stage, except for the Vienna project, which was already owned by MidAmerican.
But construction has now started at all of the sites, MidAmerican said, with the last one expected to be online by the end of 2015.