Burnley defender Daniel Lafferty has agreed to extend his loan spell at Rotherham until the end of the season.
Borussia Dortmund defender Mats Hummels has denied making any promise to join Manchester United.
The 26-year-old signs from Houston Dynamo, who he helped to two consecutive Major League Soccer Cup finals.
Manager Derek Adams told the club's official website: "Our interest in Andre has been no secret and when you look at his record that's no surprise.
"Despite still only being a young player, he's got experience of playing in Europe as well as at a top side in the MLS which is now an extremely good league which features world class players.
"Signing players from outside the EU does involve a lot more work in the background to secure the necessary clearance and visas, but this work has now secured us a player who will undoubtedly add to the squad here at Ross County."
Hainault joins Ivan Sproule, Evangelos Ikonomou and Steffen Wohlfarth in signing for the Dingwall side this month.