2009 Kansas City Chiefs season

The 2009 season was the Kansas City Chiefs' 40th in the National Football League (NFL), their 50th overall, and their first under head coach Todd Haley and general manager Scott Pioli. The Chiefs attempted to improve on their 2–14 record from 2008 with the third overall selection in the 2009 NFL Draft. In 2009, the Chiefs also honored the induction of Derrick Thomas, the team's former linebacker from 1989 to 1999, into the Pro Football Hall of Fame. Thomas' jersey number 58 was officially retired by the franchise after having been unissued since Thomas' death in 2000.

The fate of head coach Herman Edwards and his staff remained uncertain after the end of the 2008 season in which the Chiefs finished with a franchise worst 2–14 record. The team was 6–26 in the past two years under Edwards, who had one year left on a four-year, $12 million contract and was lobbying to be allowed another year to get his rebuilding movement off the ground. Team owner Clark Hunt voiced his support of Edwards, but he had also said the new general manager Scott Pioli would have "significant input" into the decision on whether to retain him. On January 23, the Chiefs fired Edwards, and on February 5, Todd Haley was hired as the 11th head coach in Chiefs franchise history and signed a four-year contract.

For the 2009 season under the Pioli/Haley regime, the Chiefs switched from a 4–3 defense to a 3–4 defensive strategy.

Although finishing the regular season last in the AFC West with a record of 4–12, the Chiefs doubled their win record from the previous season. The Chiefs did not have a single player named to the Pro Bowl for the first time since 1978 and only the 3rd time in franchise history.