Originally known as 'Maley,' the town was founded in 1880 as a whistlestop on the Southern Pacific Railroad. It was renamed in honor of a visit by the General Orlando B. Willcox in 1889. In the early 20th century, Willcox had the distinction of being a national leader in cattle production. Agriculture remains important to the local economy, but Interstate 10 has replaced the railroad as the major transportation link, and much of the economy is now tied to the freeway.
According to the United States Census Bureau, the city has a total area of 15.8 km² (6.1 mi²). 15.5 km² (6.0 mi²) of it is land and 0.3 km² (0.1 mi²) of it is water. The total area is 1.96% water.
As of the census2 of 2000, there are 3,733 people, 1,383 households, and 947 families residing in the city. The population density is 240.2/km² (622.3/mi²). There are 1,652 housing units at an average density of 106.3/km² (275.4/mi²). The racial makeup of the city is 74.95% White, 0.70% Black or African American, 1.61% Native American, 0.83% Asian, 0.05% Pacific Islander, 17.63% from other races, and 4.23% from two or more races. 41.71% of the population are Hispanic or Latino of any race.
There are 1,383 households out of which 34.3% have children under the age of 18 living with them, 51.6% are married couples living together, 12.2% have a female householder with no husband present, and 31.5% are non-families. 27.5% of all households are made up of individuals and 13.2% have someone living alone who is 65 years of age or older. The average household size is 2.65 and the average family size is 3.25.
In the city the population is spread out with 29.4% under the age of 18, 8.1% from 18 to 24, 24.4% from 25 to 44, 22.2% from 45 to 64, and 16.0% who are 65 years of age or older. The median age is 37 years. For every 100 females there are 95.9 males. For every 100 females age 18 and over, there are 92.5 males.
The median income for a household in the city is $24,334, and the median income for a family is $31,411. Males have a median income of $30,281 versus $15,532 for females. The per capita income for the city is $11,815. 27.0% of the population and 21.6% of families are below the poverty line. Out of the total people living in poverty, 36.6% are under the age of 18 and 24.6% are 65 or older.