There are two distinct species of eland: (1) the Lord Derby's Eland (Tragelaphus derbianus) and (2) the Common Eland (Tragelaphus oryx).
Lord Derby's is restricted to the west African and north central African regions: CAR, Cameroon, just into Chad and Sudan, and also Guinea, Senegal and the junction of neighbouring countries. The Common is has a wider range, across southern Africa and along the eastern side of the continent, perhaps as far up as the southern tip of Sudan and Ethiopia.
The Common Eland has three recognised subspecies if you do some basic research: Cape Eland in the south, Livingstone's in the north of their range, and East African along the north east of the range. As a matter of interest, the East African Eland is also known as Patterson's Eland. If you do a lot of research you will find reference to other "subspecies" but the taxonomic variance is largely that they are isolated populations (such as Tragelaphus oryx kaufmanni in the Caprivi). They all fall under the species of Common Eland.