Middleton was named for its location between the old fort Boise and Keeney's Ferry; it being the midpoint between the two. It served as a rest stop for those heading for Keeney's Ferry. It had a stage station in the early days of the Oregon Trail, a post office in 1866 and a water powered grist mill in 1871. The Ward Massacre occurred near the site in 1854. Middleton is the oldest settlement in Canyon County, with the land being parceled out in 1863 by William N. Montgomery. The Boise River flooded in 1872 and cut a new channel, isolating the town on an island; as a result, the town moved to a new location in the years after 1880. The town incorporated as a city in 1910, although the certificate was not issued until 1971. The present mayor is Steve Rule. On February 1, 2007, 78% of Middleton High School burned down, caused by the overheating of a fan above the weight room. The 42-year-old building was built when fire codes required sprinklers to be installed, but there was no provision for their functionality. To save money during the construction of the school in the 1960s, the sprinklers were installed but were never connected to a water source.
At the 2010 census there were 5,524 people in 1,843 households, including 1,392 families, in the city. The population density was. There were 2,037 housing units at an average density of. The racial makup of the city was 92.5% White, 0.3% African American, 0.6% Native American, 0.5% Asian, 0.1% Pacific Islander, 3.3% from other races, and 2.8% from two or more races. Hispanic or Latino of any race were 10.0%. Of the 1,843 households 49.5% had children under the age of 18 living with them, 54.7% were married couples living together, 13.6% had a female householder with no husband present, 7.2% had a male householder with no wife present, and 24.5% were non-families. 19.9% of households were one person and 7.1% were one person aged 65 or older. The average household size was 3.00 and the average family size was 3.45. The median age was 30.5 years. 35.1% of residents were under the age of 18; 7.6% were between the ages of 18 and 24; 29.9% were from 25 to 44; 19.1% were from 45 to 64; and 8.2% were 65 or older. The gender makeup of the city was 49.9% male and 50.1% female.
At the 2000 census there were 2,978 people in 1,017 households, including 755 families, in the city. The population density was 1,696.8 people per square mile. There were 1,066 housing units at an average density of 607.4 per square mile. The racial makup of the city was 91.67% White, 0.30% African American, 1.07% Native American, 0.24% Asian, 0.24% Pacific Islander, 3.53% from other races, and 2.96% from two or more races. Hispanic or Latino of any race were 10.21%. Of the 1,017 households 43.8% had children under the age of 18 living with them, 57.6% were married couples living together, 11.6% had a female householder with no husband present, and 25.7% were non-families. 18.5% of households were one person and 6.9% were one person aged 65 or older. The average household size was 2.93 and the average family size was 3.35. The age distributionwas 34.2% under the age of 18, 10.4% from 18 to 24, 31.9% from 25 to 44, 15.8% from 45 to 64, and 7.7% 65 or older. The median age was 28 years. For every 100 females, there were 97.9 males. For every 100 females age 18 and over, there were 94.9 males. The median household income was $32,665 and the median family income was $34,734. Males had a median income of $27,298 versus $20,792 for females. The per capita income for the city was $12,447. About 7.5% of families and 10.4% of the population were below the poverty line, including 12.8% of those under age 18 and 16.5% of those age 65 or over.
