In my experience dealing with depressive patients, a question that frequently arises - especially from people who have just got started with their treatment - related to whether depression is a mental illness. The simply and short answer is "Yes", but the REAL question that should arise here is... why should this be a concern, in the first place?
So what if depression is a mental illness?
Even though we're in broad XXI century and despite the fact we live in a supposedly advanced society, it's appalling just how we're still infantile in our beliefs, and held back by inexplicable peer pressure at social-wide levels.
Did you know that many people suffering from depresson refuse to seek treatment for depression because they're afraid to admit they have a problem? And generally when someone wants to keep this kind of problem a secret, it's because they're afraid to admit they may have a mental sickness... as though it would imply they're no longer capable of holding up to their past accomplishments and present responsibilities.
You may not quite understand this from your current point of view... but that reasoning is just as silly as being afraid to see a MD because people might criticize you, or look at you funny, for being physically sick. Wouldn't that be a lot crazier than looking for a cure?
Important things to consider about this illness
You must keep in mind that depression IS a mental illness, and a serious one at that. It could keep getting worse until you're fully deprived of your ability to enjoy life or function normally. Further, you must keep in mind that being a sickness, it's a medical problem -- not a fault in character.
Finally, you should know that as many as 10% of the people in the USA has already admitted to having problems with depression, and sought treatment for it. And quite likely the actual percentage of people who silently suffer from this illness is much, much higher... but many people are still too afraid to admit they're having this problem, which only adds to their personal drama. What's the point of that, really?