Theodoric I of Lower Isenburg (German: Dietrich I. von Nieder-Isenburg) was the Count of Lower Isenburg from 1218 until 1253. Theodoric received the territories which were to become Lower Isenburg, as opposed to those which were to become Wied with the other line of Isenburg-Braunsberg, with the partition of Isenburg-Isenburg in 1199. he was succeeded by Theodoric II in 1253.