W.A. Irwin came from Santa Monica, California, where as a developer, he owned thousands of acres and established colony tracts. He laid out Irwin City, which was surveyed by George Manuel, and had it recorded on May 8, 1907. The colony was less than a mile south of present day Hilmar. Irwin himself promoted the area in brochures claiming the climate was the best in the world. No hard winters, no snow storms, no cyclones, only eternal summer.
Irwin City had a hotel, bakery, jeweler and barber. Other businesses were Hedman-Johnson Meat Market, Johnston Hardware and Ceylon Grocery. A.H. Boothry and sons ran a general merchandise store. The building known today as Irwin City antiques was previously Pedigo's Store and later Klint's Hardware. Nearby was a two story building with the intriguing name Fallen Angel Saloon. The upper floor was a hotel.
In 1911 a U.S. Post Office opened in Thomas Pedigo's General Store and operated until 1958. Pedigo was postmaster and later became a circuit judge for the area.
In 1917 the Tidewater Southern Railroad line reached the area. The railroad laid out the town of Hilmar just to the north. Irwin City began to be absorbed by Hilmar as it grew southward but it refused to disappear. There are a number of businesses and organizations today using the term Hilmar-Irwin. Train service halted in 1954 and trucks took over transporting farm produce. What was once two competing towns became one.