Delmas earned defensive Rookie of the Month honors for September of 2009. He recorded his first career interception in Week 9 against the Seattle Seahawks. In Week 15 against the Cardinals, Delmas returned an interception 100 yards for a touchdown. It was the third-longest interception return touchdown in Lions history.
With the interception return, Delmas became the first rookie in NFL history to record a safety and score touchdowns on fumble and intercpetion returns. He finished his rookie season with 94 total tackles and two interceptions.