Being mentally ill, as opposed to having a mental disorder, is a close distinction. When you say someone is ill, it usually implies they are sick or non-functioning. There are also abnormalities in thought processes, mental state, and mood. A person who is mentally ill may or may not be treated by a psychiatrist who may or may not be prescribing certain medications to help with the illness. These are people who have difficulty maintaining interpersonal relationships and are often traumatized by an event or something that happened in their life, which rendered them disabled.
Mental disorder can be defined by a unique set of behaviors and is more defined. However, not all people who have mental disorders are mentally ill. People with a disorder are typically responding well to treatment and do not require constant supervision or hospitalization. They generally are on certain medications that control the disorder. Mental disorders are related to anxiety issues, phobias, panic disorders, and general depression.