The ileum is located after the jejunum and can be up to three meters. It is hooked up in the abdomen through the mesenteria. Blood supply is transported via the Arteria mesenterica superior. There is no clear border between ileum and jejunum, it is a continuous transition.
The ileum does look a little paler and is slightly thinner. Additionally the mesenteria in the ileum contain more fatty tissue. The most important difference is the existence of Payer Plaques in the ileum.