On August 22, 2000, at approximately 1410 central daylight time, N785AN, a Boeing 777-223 operated by American Airlines as flight 154, encountered unexpected turbulence, while descending from FL260 to FL190 near the DELLS (DLL) VORTAC in Baraboo, Wisconsin. One flight attendant was seriously injured. The 4 cockpit crewmembers, 11 additional flight attendants, and 235 passengers were not injured. The airplane was not damaged. The 14 CFR Part 121 flight was operating in instrument meteorological conditions at the time of the encounter and the flight was on an IFR flight plan. The flight originated from the Narita Airport, Tokyo, Japan, and continued on to its intended destination of Chicago, Illinois, where it landed without incident. The captain reported the seatbelt sign was on when they encountered unexpected moderate to severe turbulence. He reported they were in instrument meteorological conditions and the radar was indicating cells to the west of their course, but not along their flight path. He reported there was a downdraft followed by an updraft and that the bank angles did not exceed 30 degrees. The first officer reported they were about 20 miles northwest of the DLL VORTAC between FL260 and FL240 when the turbulence was encountered. He reported, "Both the Captain and I had our radar on. My radar indicated nothing other than light precipitation between our position and the VOR. We first encountered what I would term as moderate turbulence. It quickly got worse. I notified ATC of the turbulence as the Captain continued to fly the airplane. A flight attendant opened the cockpit door to inform us that one flight attendant had been injured." Both relief first officers were in the back of the airplane when the turbulence was encountered. They both reported that they were thrown to the floor at the time. One of the relief first officers reported, "The seat belt sign was on and all passengers were seated. The flight attendants were preparing the cabin for landing. The #11 flight attendant apparently injured her foot. I and another flight attendant secured the #11 flight attendant to a jump seat and put an ice pack on her foot. I instructed all other flight attendants to remain in their seats. I returned to the cockpit, and the Captain made the prepare for landing P.A. and reminded everybody to remain seated." The flight attendant who was injured sustained a fractured cuneiform bone in her foot.