People will always judge sadly, as evidenced on this thread. I'm not a single mum but I became pregnant with DD fairly soon after moving in with DP. We were actually together a couple of years but had lived abroad for most of that time and kept the relationship fairly low key.
Anyway, I was most definitely judged! Despite being happy about the pregnancy, in my 30's, educated to master's level, financially secure etc. etc. I got some very rude comments.
The most disappointing source of judgment was my sister. She was outwardly very supportive and never once said anything negative while I was pregnant, and is what I would have considered a very open minded person. However, one night when DD1 was about two (so I had thought any judgement would have long passed) I complained about DP in a lighthearted manner, I can't even remember what I was actually complaining about but it really was lighthearted. She'd had a considerable amount of wine and just said in a really nasty way "what do you expect when you had a baby with someone you barely knew?" I was so floored. For a start, by the time DD was born I'd known him more than 4 years so he was hardly a stranger, but regardless the judgment was so unnecessary and so harsh. I argued back but she kept insisting I "barely knew him" until I left in tears (I am NOT a crier).
I'll never know what got into her and she never apologized. I imagine she was mortified the next day so tried to pretend it never happened, but our relationship will never be quite the same. If my own sister, who I was always very close to, can judge like that I can only imagine what other people said/thought.
We're still not married and have had another DC and I know that drives people batty too! I've been asked more times than I can count when we're going to get married. Suffice to say I can only imagine the judgment single mums get. Horrendous.