The name "Hertsmere" was invented for the new district by combining the common abbreviation of "Hertfordshire" ("Herts") with "mere", an archaic word for boundary. The name is doubly appropriate as the district straddles the historic county boundary between Middlesex and Hertfordshire and forms the administrative boundary between Hertfordshire and Greater London. The name is reflected in the council's coat of arms, which shows a hart upon the battlements of a boundary wall.
The district was awarded borough status by Royal Charter in 1977.