The former Everton and Manchester United striker has signed an initial 18-month contract with the option of another year.
The 33-year-old will also work as a coach with the first team and academy as he strives towards his goal of becoming a manager.
In a statement on Derby’s website, Rooney said: "I'm very excited about the opportunity that Derby County have provided me with.
"I'm looking forward to joining Phillip Cocu, his coaching staff and the first-team from the start of January.
“I'm sure I can make a big contribution."
Rooney will return to England after spending almost two years at MLS side DC United.
He retired from international football in 2018, after becoming his country’s all-time top scorer with 53 goals.