Jack Lord lived in Beverly Hills when he was asked at the last minute to read for the part of McGarrett. He read for it on Wednesday, flew to Hawaii on Friday, and was in front of the cameras the following Monday. This changed his life. He would become a permanent resident and prominent figure in Hawaii, contributing to many local causes and charities, and often mentioned publicly in consideration for political office. After he died, a fan-funded bust of him was erected in Honolulu.
The show was originally to be about a house detective for a chain of hotels in Hawaii. The network thought that would limit the storylines to areas affecting only the hotel chain, so it suggested that the main character be in charge of a Hawaii State Police unit, which would allow the show to expand its coverage to crimes committed all over the islands. Unfortunately, Hawaii at the time didn't have a State Police agency, but the network decided to go ahead with the idea anyway.
McGarrett's office was in the Iolani Palace, the actual palace used by the last Kings and Queens of Hawaii. In 1969 the Palace had fallen into disrepair after years of abuse and neglect. It has since been restored, and can now be toured for $20.
Kam Fong, who played Det. Chin Ho Kelley, was a real-life Honolulu police officer from 1946-62, when he retired for a career in real estate.