This is designed to help those who may have it glitched:
Firstly, mine was glitched. Or, I thought it was. I got it to pop, if this doesn't work for you, my apologies, it just what worked for me. The reason I'm posting this, is some people are saying it is either gonna work for you or it won't. Well it didn't work for me, yet in the end I got it, so that's not the case.
After getting over a hundred kills I decided it was glitched. I then wondered why it would work for some, so I started making assumptions on how the coders intended it.
Firstly, the two most popular methods seemed to be either:
A) dropping mines and blowing up chasing police/enemies
B) farming at the police station in French ward
So I made two basic assumptions as to why these aren't counting.
A) kills in a car do not count as enemies. I'm guessing the game notices the cars destruction, and counts it as a vehicle kill rather than enemies killed.
B) the police are not enemies. They are friendly (blue colour) until aggravated. If you blow them up when they aren't hostile, they aren't registered as enemies.
my steps :
I don't know if it's all required. It's just what I did.
I deleted my game and redownloaded it. I deleted my saved data. (This resets the games cache - it helped with a glitch on forza so I did it here).
Replayed the game til I had access to the mines.
I didn't kill a single person, except red hostile enemies on side missions or red hostile enemies clustered around the city. I killed no police. I killed no one in cars. All 30 of my kills were in New Bordeaux, not the Parish.
I kept a tally on how many I had, and the achievement popped bang on 30.
If this doesn't work, then maybe it's just glitched. But it worked for me after 100+ kills with no luck.
Hopefully it helps. If it does, please vote positive. If it doesn't, don't vote negative or I'll just remove it. I'm just trying to help.