I knew there was a difference but never bothered to check. A friend just shared a link that finally answered my question and probably many of you out there, too.
"A journal is much more personal than a diary. A journal contains feelings, emotions, problems, assurances and is pretty much used to examine one’s life. Diary writing is a daily activity whereas journal writing can be done whenever the writer feels the need to write."
Gratified to note that I keep both, though the journal contains more sketches and graphics than text.