CTU Domestic Units are field offices covering operations within a single city or metropolitan area. Domestic Units report directly to Division Command, but are also subject to review and interference from District Command.
CTU New Orleans: Jack Bauer contacted CTU New Orleans in order to check into the sudden disappearance of Robert Ellis, who was murdered during a telephone conversation with Jack and David Palmer.
CTU New York: Found a vial of the Cordilla virus along with the New York Police Department. The vial was attached to a railing but was defused. ("Day 3: 11:00am-12:00pm"). By the time Day 8 began CTU New York is shown for the first time and Chloe O'Brian works there.
CTU Phoenix: CTU Phoenix also sent a helicopter to back up Jack Bauer during the events of One Shot.
Phoenix is only seen on screen and not mentioned. For Las Vegas, Denver, and Phoenix, it is not stated explicitly that a Domestic CTU Unit found the vials of the virus (these could have been the FBI or other law agencies working in tandem with CTU). However, since these are large U.S. cities, it makes sense that each would have a domestic unit.
A note on the following: CTU Denver, CTU Las Vegas, CTU Phoenix, CTU Seattle. During "Day 3: 11:00am-12:00pm," CTU Los Angeles coordinated with numerous other law enforcement agencies to bring down the bio-terrorism ring of Stephen Saunders by capturing and killing his Cordilla virus couriers. It was not explicitly stated that these operations were carried out by CTU TAC teams (these actions could have been carried out by police SWAT teams, FBI agents, or other groups working in tandem with CTU).