[Campion]

Canon law pre 1983 had the concept of illegitimacy -- it was an impediment to ordination to the priesthood -- but the children of a putative marriage (one entered into in good faith by at least one party) were always considered legitimate.

Post 1983, you are correct that "illegitimacy" does not have any meaning in canon law.

[firebrand]

I was told this by a priest at St. Patrick’s in 1977. He never mentioned the priesthood business. (I had to take lessons when I went back to the Catholic church, since I was brought up pre-Vatican II.)

[maryz]

There have always been illegitimate babies but it’s still merely a civil category. Illegitimacy as an impediment to the priesthood was merely a practical consideration on the theory that if the parents couldn’t control themselves, there was a good chance the illegitimate son wouldn’t be able to either — at least that’s how they explained when I was in high school. I’m not sure it was an absolute impediment or if individual cases could be exceptions.