The Honolulu Police Department occupied the old Sears & Roebuck building on Beretania Street during Five-0's years. Acquisition was made in 1967, the building was converted from open floor space suitable for sales and into divided spaces suitable for a police department. Above, we see how the main entrance appeared in "Draw Me a Killer" (Season 6). Below, we see (as Honu pointed out in a Guestbook comment) escalators that look much more like they belong in a department store than in a police department.
Below, we see how the exterior of the building appeared in 1954.
The building is known to date back at least as far as the mid- 1940s,
although the art deco details might cause us to wonder if it wasn't
built in the 1930s.
Today, the HPD occupies a larger building on Beretania Street. It, too, possesses art deco details, although the HPD has remained silent on inquiries into its history.
The HPD has a museum in their headquarters building. There's even a display honoring Hawaii Five-0. Yes, that's Kam Fong Chun, who portrayed Five-0 Detective Chin Ho Kelly, in the top-left display photograph. In real life, Kam was an HPD officer for 16 years.
Nor was Kam the only HPD officer to appear on Hawaii Five-0. Whenever HPD officers were needed for the show, real-life officers were hired to play cameo roles. As one source said, an HPD officer could be moving barricades one moment, then appearing in a scene the next.
An interesting point about both Five-0's portrayal of the HPD and how it is (and was) in real life: Quite often, privately owned vehicles are used by patrolmen. As we see on the show, they simply attached a bubble light to the roof of their cars and went to work. It would be interesting to know whether the privately owned patrol cars seen on the show were actually used on HPD patrol assignments.