William Siemon became a produce and general merchant c1872. Prior to this time he had been a fruiterer in a different location in Brisbane Street. The wholesale and retail grocery and produce business was located in the Top of Town area, next to F. W. Johnson's City Coach Works at 231 Brisbane Street. W. Siemon & Sons dealt in seeds, seed potatoes, poultry, pigs, cattle, maize, chaff, lucerne and the like. The fact that the family owned over 300 acres at Walloon where cows were bred and pigs slaughtered would have been a benefit to their in-town operations, providing animals and crops to sell. The property was known as Prospect Hill Jersey Stud Farm where prize-winning cows were produced and subsequently exhibited at shows. They also produced dairy products, owning a butter factory named Prospect Hill Butter Factory.  Behind their shop in Brisbane Street, W. Siemons & Sons had their own railway platform where produce could be sent and received efficiently by train.  This feature is remarkable and probably indicates the power, affluence and success of the family business. 

Around 1880, William Siemon purchased two acres of land at Leichhardt and built a house at 29 Siemons Street, which is considered of historical significance. William's son George purchased this house in 1885. Several years later, William and much of the family left Ipswich to expand the company into Brisbane and North Queensland. George remained to manage the Ipswich branch of the family firm. 

Circa 1906 Siemons also had a bulk store in Brisbane Street, just opposite the Baptist Church, near the Union Hotel. In 1907, the family created a new company, W. Siemon & Sons Ltd. that was registered in Brisbane. The new limited liability company of general merchants and graziers would take over and acquire W. Siemon & Sons. Shares were to be divided between family members. In 1911 Prospect Hill farm and butter factory were offered for sale.

After George Siemon died in 1924, following an extremely short retirement, the Ipswich branch of W. Siemon & Sons Ltd closed, although the company remained in Brisbane. The family property adjoining the Old Flour Mill was sold to F. W. Johnson in 1925. 

W. Siemon & Sons racked up more than fifty years in business in Ipswich.