A populated area south of the peninsula itself, which was initially housing for the Hydro employees, is also considered part of Herøya as a suburb of the city of Porsgrunn.

The construction of the plant by Norsk Hydro in partnership with the Luftwaffe-operated Nordische Aluminium Aktiengesellschaft (Nordag) was however ended on 24 July 1943, when a bombardment by American B-17 Flying Fortresses completely destroyed the facilities as well as hitting parts of the surrounding areas, killing 55 people, including civilians.

Fra en oppvekst i forrige århundre by historian Harald Berntsen, portrayals are given of incidents and milieus in Herøya, from the time when his family moved there in 1951 (from downtown Porsgrunn), just before he was to begin school, and until 1960.

Berntsen's family lived in a flat on Torggata, on the peninsula proper, to the west of the Gunneklevfjord, in a recently built 4-flat house which the father had been given by Hydro.

The yards end in a fertile belt of tall, wavering rushes with a forest of brown cigars on the top, in front of the enclosed Gunneklevfjord, glittering in the sun in all hues of pollution.

The engineers lived in the "'engineer town' consisting of villas with spacious gardens having been situated facing the still idyllic Frierfjord, closest to the factories, when Hydro's plant on Herøya grew from 1928 on.

Or they would occupy the row of Hydro's more elegant one-family houses for engineers at Bakkedammen and, in a few cases, the grand workers' villas in Adriansåsen, the hill atop Herøya.