Welcome, Puggle and thanks to others for your insight.
I've been dealing with (sometimes!) depression for 12+ years now. When I first 'came out' in 2002-03 to close friends and trusted colleagues, I found that fully 80% of them either had someone close to them with a MI or had a MI themselves, either in the past or ongoing. Maybe that's partly influenced by my profession (currently on hold) which I won't talk about here.
Fortunuately, partly because its prevalence is becoming known, mental illness is less stigmatised now than it was when I first admitted to myself that I had a real problem. And there's no comparison with the 1980s when, in hindsight, I actually felt it.
Having said all of that, there's still a long way to go. There will always be a proportion of people who will glibly tell you to 'cheer up' or that 'you've nothing to be depressed about'.
I think part of it is that people who suffer from MI look like everyone else most of the time. This is simultaneously a good thing and a bad thing. On the positive side, we are often free to get on with our business without getting hassled or patronised. But then, because the additional weight we carry is invisible, we are often also asked to do more, at the expense of taking care of ourselves.