In the US why are they attacking Chicago specifically?

I'm American, I live in Illinois which is a pretty blue state from what I can tell, so it completely baffled me when Trump announced he was going to attack Chicago for mass deportation. I'm white, so I personally don't have anything to worry about but all my friends are not. His plans to not only deport immigrants with visa but also American born citizens is completely ridiculous and I don't even see how that would be possible but after inauguration, idk. I know we have quite a big Latino population, but is it big enough to warrant this? I may be missing something but it's just completely out of the blue for me. Could someone tell me why this is? Why Chicago specifically?