The 9th Infantry Division () was a unit of the Polish Army in the Second Polish Republic. The division was originally formed in 1919. Stationed in Siedlce, it took part in the Polish September Campaign under Colonel Józef Werobej. There, General Władysław Bortnowski ordered three Polish units - 9th I.D., the 27th Infantry Division, and Operational Group “Czersk” - to counterattack on the morning of September. However, communication between 9th I.D. and 27th I.D. failed and the offensive was a failure, with the German 3rd Armored Division managing to halt it.