Helmut Jahn, 81

 

 Helmut Jahn, a German-born architect who designed buildings around the world but was most influential in his adopted hometown, Chicago, where he conceived of an extravagant downtown home to state government and the United Airlines terminal at O’Hare International Airport, died on Saturday in a traffic accident near the horse farm where he lived, in St. Charles, Ill. He was 81.

 

 His wife, Deborah (Lampe) Jahn, confirmed the death. He had been riding his bicycle in suburban Campton Hills when he was struck by two cars that were heading in opposite directions.

 

 Mr. Jahn and his wife, Deborah owned Seven Oaks, a landmarked 30-acre American Saddlebred horse farm in St. Charles, Illinois, that dates to the 19th century.

 

 In addition to his wife, whom he met when she was the interior designer for McCormick Place, Mr. Jahn is survived by his son, Evan, a partner in the firm; two granddaughters; and a brother, Otmar.