The town became less isolated in 1911 when the first telephone service was installed. Hummock Hill became Whyalla when the town was officially proclaimed on 16 April 1914 and Whyalla's first policeman arrived three weeks later. The following year, the ore conveyor belt on the jetty became operational and more ore was able to be loaded onto the ships. BHP had begun to build a steelworks in Newcastle and the ore produced at Iron Knob way was now being sent there to produce steel.
In the following years, Whyalla's population grew slowly but steadily, and by 1920 it had reached approximately 1,000. The facilities that were the central focus of country towns, of this time, were beginning to appear. The Whyalla Institute on the corner of Jamieson and Gay Streets was opened by Mr G E Delprat on 3 November 1920 and the Kelly Street church was built. Sporting associations were being formed, as well as an RSL sub-branch. In subsequent years BHP provided a dairy, a new power house, a desalination plant and a power line to Iron Knob. The Whyalla Brass Band was formed, the first bank opened and a freight service to Adelaide began.
Most of this development took place at the immediate base of Hummock Hill, in an area bounded by Gay and Horwood Streets to the south and McBryde Terrace to the north. A large part of this early section of town no longer exists, with little evidence of where it had been.
Eighteen years later, in 1938, the town's population had only grown by another 400 residents, but the catalyst for a rapid increase had already been set in place the year before. The BHP Indenture Act was proclaimed in 1937 and an area of land was set aside for the construction of a blast furnace and harbour. Concern was expressed about the shortage of water at the site and negotiations with the SA Government resulted in the commitment for the construction of a pipeline from the River Murray.
As construction of the harbour and blast furnace commenced in 1939, world tensions were rising with the imminent outbreak of World War ll. The Royal Australian Navy asked BHP if they were able and willing to build patrol ships, and so the construction of shipyards next to the blast furnace site was also to begin. All of this work required labour and the influx of workers into the town saw the population rise drastically, as did businesses and facilities for the residents. In 1940, the Whyalla Hospital, the Whyalla Abattoirs, the RAOB Hall, the Ozone Open Air Cinema, St Teresa's School, and the Bayview and Spencer Hotels were all opened or being built. The Whyalla News was established, and the shipyards began work.