Eberhard I of Isenburg-Grenzau was the Count of Isenburg-Grenzau from 1287 (1286) until 1290. Eberhard was one of three sons of Count Henry II of Isenburg-Grenzau. In 1286 Henry partitioned his realm between his sons, with Eberhard's brother Louis' domain being called Isenburg-Cleberg and his other brother Gerlach's domain being called Isenburg-Arnfels. Eberhard was to receive Grenzau. The following year Henry died. Eberhard died in 1290 and without any children his realm passed to his brother Louis.