Growing up in Nashville, Hillenmeyer attended Harding Academy before moving onto Montgomery Bell Academy. Hillenmeyer was a two-time All-state, All-region and All-district selection at Montgomery Bell Academy playing linebacker, defensive end, tight end and punter for the Big Red, including the school's 1998 state championship team. He lettered 3 years in football, 3 years in track and 2 years in tennis.
College career
Hillenmeyer was a four-year letterwinner at Vanderbilt where he saw action in 45 games, starting the final 23 and tallying 249 tackles and 6.5 sacks. As a senior, Hillenmeyer was 1 of 6 Division I-A football National Scholar-Athletes earned First-team All-SEC and First-team Academic All-America honors while leading nation in tackles per game.
Professional career
Hillenmeyer signed with the Bears after being cut by the Packers at the end of the 2003 preseason. Hillenmeyer spent most of 2003 playing special teams for the Bears, he tied for 5th on Chicago with 12 special teams tackles as a rookie, playing 13 games on special teams. He became the starter at strong side linebacker in 2004 starting 11 games while appearing in all 16 and making 90 tackles and 2.5 sacks. In 2005, he had 71 tackles including 5 TFLs, 1 sack, 1 INT and 2 PBUs while starting 12 of the first 13 games at SLB before a thumb injury sidelined him for the final 3 regular season games. On June 30, 2006, the Bears signed Hillenmeyer to a five-year, $13 million contract extension through 2010 that included a $5 million signing bonus. That season, he started 13 games at strongside linebacker, finishing with 68 tackles, 2 TFLs, 1 fumble recovery and a career-high 3 PBUs. In 2007, he played in all 16 games for the second time in his career, starting a career-high 14 contests and had a career-high 101 tackles, and registered 5 QB Hits, 3 TFLs, 2 PBUs, 1 forced fumble and 1 fumble recovery. In 2008 Hillenmeyer played 13 games, starting six. Along with All-Pro linebackers Brian Urlacher and Lance Briggs, the Bears were thought to have one of the best linebacking corps in the league. The Chicago Sun-Times has called Hillenmeyer "underrated". Hillenmeyer replaced Brian Urlacher at middle linebacker for the Bears after Urlacher's season-ending wrist injury in Week 1 of the 2009 season, making 90 tackles, 2.5 sacks, 1 interception and forcing four fumbles. On September 14, 2010, Hillenmeyer was placed on the Bears injured reserve list after sustaining a severe concussion in the team's season opener against the Detroit Lions. He was released by the Bears on February 28, 2011.
