Middleton is located at 43°42'23" North, 116°37'13" West (43.706353, -116.620228)^GR1.

According to the United States Census Bureau, the city has a total area of 4.6 km² (1.8 mi²). 4.6 km² (1.8 mi²) of it is land and none of it is covered by water.

As of 2000, there were 2,978 people, 1,017 households, and 755 families residing in the city.

There were 1,017 households out of which 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 all households were made up of individuals and 6.9% had someone living alone who was 65 years of age or older. The average household size was 2.93 and the average family size was 3.35.

In the city the population was spread out with 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% who were 65 years of age 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 income for a household in the city was $32,665, and the median income for a family was $34,734. Males had a median income of $27,298 versus $20,792 for females. The income for the city was $12,447. 10.4% of the population and 7.5% of families were below the poverty line. 12.8% of those under the age of 18 and 16.5% of those 65 and older were living below the poverty line.