What police departments have counter-terrorism units?

I read about ISIS/al-Qaeda TTP as a hobby, and take classes on counterterrorism just because. After the San Bernardino shootings, I really want to put my knowledge and experience to use. Does anyone have any recommendations as to police or other agencies who have counter-terror departments?

I already know about the CIA and FBI, but thanks for suggesting them as well.

Also, I'm in my mid forties.