The Chisholm Trail passed to the east of Duncan prior to the town's founding. An estimated 9,800,000 Longhorn cattle were herded up the trail between Texas and Abilene, Kansas during its existence. After learning that an extension of the Chicago, Rock Island and Pacific Railroad was being built from Kansas to Texas, Scotsman William Duncan brought his wife, parents, and other relatives and created a trading post situated at the intersection of the north-south Chisholm Trail and the east-west military passage between Fort Arbuckle and Fort Sill. The first train arrived on June 27, 1892; that date is considered the official birthdate of the town.
Centrally located in Stephens County, Duncan was made the county seat in the first years of the 20th Century. As a compromise between residents of the northern and southern parts of the county, the county courthouse was located in the middle of Duncan's Main Street, half of it in the northern part of the city and county and half in the southern. Main Street made a wide circle around it on both ends.
Duncan once adopted the slogan, "The Buckle on the Oil Belt." Its main claim to fame is as the birthplace of the Halliburton Corporation. Erle P. Halliburton perfected a new method of cementing wells, making oil production much easier and more profitable, and established the New Method Oil Well Cementing Company in 1919. He died in 1957, at which time the company had 201 offices in 22 states and 20 foreign countries. Halliburton maintains seven different complexes in Duncan plus an employee recreational park, but the corporate offices relocated first to Dallas and later to Houston.
There were 9,406 households out of which 28.8% had children under the age of 18 living with them, 54.6% were married couples living together, 10.4% had a female householder with no husband present, and 31.7% were non-families. 28.9% of all households were made up of individuals and 14.7% had someone living alone who was 65 years of age or older. The average household size was 2.35 and the average family size was 2.88.
In the city the population was spread out with 24.1% under the age of 18, 8.3% from 18 to 24, 24.8% from 25 to 44, 22.6% from 45 to 64, and 20.2% who were 65 years of age or older. The median age was 40 years. For every 100 females there were 89.8 males. For every 100 females age 18 and over, there were 85.3 males.
The median income for a household in the city was $30,373, and the median income for a family was $37,080. Males had a median income of $31,173 versus $19,731 for females. The per capita income for the city was $17,643. About 28.7% of families and 27.4% of the population were below the poverty line, including 22.1% of those under age 18 and 42.8% of those age 65 or over. Duncan, with its neighboring towns and their distances