Where do fleas and ticks live?

I lived in a wooded area growing up, so finding fleas or ticks on our pets was pretty normal. There was a lot of wildlife, including deer, so it made sense to me that there was a high risk for our pets living in that area.
I do use preventative treatments for my pets now, of course, but I live in the city. I found my cat chasing a tick across my kitchen floor last night – where do they come from? Do they just live in the grass?