The midfielder joins Frank Yallop's side from Hozerla Uzhhorod in Ukraine.
The MLS outfit will be Cocis' eighth stop since leaving Cluj, the club where the 31-year-old developed his game as a young player. His most recent squad is Ukrainian side Hoverla Uzhhorod.
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Though he has seen his time with the national team diminish, Cocis has 50 caps with Romania and went the full 90 in Romania's 3-1 loss to Greece in the first leg of a World Cup qualification playoff in November 2013.
“I’m happy to be joining the Fire and can’t wait to get started,” Cocis said in a news release. “I think the move will suit me well as I enjoy big cities and Chicago is especially charming. The team is really coming together and I’m looking forward to contributing to its successes for the remainder of the season.”