Kenworth began its history in Portland, Oregon. In 1912, the company was founded by brothers George T. and Louis Gerlinger, Jr. as a car and truck dealership known as Gerlinger Motor Car Works. In 1914, they decided to build their own truck with a more powerful inline six-cylinder engine. This was the first ever put into a commercial truck. The Gersix, as it was known, unveiled in 1915, was framed in structural steel, which along with its power, made the truck ideal for the rugged Northwest, where it was used for logging. In 1916 the Gerlinger Motor Car Company moved to Tacoma, Washington. Seattle businessman Edgar K. Worthington was managing his mother's commercial building, where Gerlinger became a tenant, and became intrigued by the Gerlinger company. Worthington's tenant was doing quite well, or so it seemed, and the Gersix became a popular fixture in the Northwest. In 1917 Worthington and his business partner Captain Frederick Kent bought the Gerlinger business, renaming it the Gersix Motor Co

In 1919 Kent retired from the business, and his son Harry Kent became Worthington's new partner. In 1922, Gersix made 53 trucks at its factory on Fairview Avenue at Valley Street. Under the new name, the company moved to 506 Mercer Street and later to 1263 Mercer Street. Trucks and motor coaches were assembled in individual bays rather than on a conventional assembly line. In 1923 Kent and Worthington reincorporated the business as the Kenworth Motor Truck Company. The name was a combination of the two names "Ken" and "Worth", the same as the surname "Kenworth". In 1926 they started making buses, and in 1933 Kenworth was the first American company to offer diesel engines as standard in their trucks. In 1945 Kenworth was bought by The Pacific Car and Foundry Company.
After Pearl Harbor, begins production of M-1 "wreckers," heavy-duty six wheel drive vehicles armed with special equipment for combat conditions. In 1943 the company begins to produce components for the B-17"Flying Fortress" and the B-29 "Super Fortress" aircraft.
In 1944 Pacific Car and Foundry buys Kenworth. Paul Pigott strikes a deal with the owners and Kenworth becomes a wholly owned subsidiary of Pacific Car and Foundry. Kenworth is still producing military in 1944 -1950 as well as commercial vehicles. Sugar plantations in Hawaii become large customers. In 1946 a new Seattle factory is opened and by 1950 foreign sales account for 40 percent of sales.
1951 - 1954 Kenworth produces the 853 for work in the oil fields of the Middle East and the 801 for earth moving in America. In 1955 the radical cab-be side-engine design is launched and becomes an instant hit.
In 1956 the 900 series is introduced and a fleet successfully transports 3,000 tons of equipment and supplies to the northern Yukon for oil exploration.