You would have to define "IED" a little better if you want it to mean something other than what it is being used to mean today. The use of improvised explosives goes back quite a long time. A famous incident that is sometimes regarded as the first "car bomb" (a wagon bomb) is was the 1920 Wall Street Bombing, for example. Mike Davis' excellent book Buda's Wagon: A Brief History of the Car Bomb is an excellent, short history of the use of "hidden" explosives (sometimes military-grade, sometimes home-made) as weapons in the 20th century. Whether you consider such things IEDs depends on your definition — the term "IED" is not especially well historically defined.