Since 1927 Shelley has been home to the "Idaho Annual Spud Day", which is celebrated on the 3rd Saturday of September. It typically features a parade, live bands, games (such as a tug of war into a pit of mashed potatoes) and free baked potatoes.
As of the census of 2000, there were 3,813 people, 1,201 households, and 989 families residing in the city. The population density was 2,884.5 people per square mile (1,115.3/km²). There were 1,253 housing units at an average density of 947.9/sq mi (366.5/km²). The racial makeup of the city was 89.93% White, 0.18% African American, 0.68% Native American, 0.26% Asian, 0.03% Pacific Islander, 6.74% from other races, and 2.18% from two or more races. Hispanic or Latino of any race were 11.78% of the population.
There were 1,201 households out of which 48.9% had children under the age of 18 living with them, 67.0% were married couples living together, 13.0% had a female householder with no husband present, and 17.6% were non-families. 15.3% of all households were made up of individuals and 7.2% had someone living alone who was 65 years of age or older. The average household size was 3.14 and the average family size was 3.50.
In the city the population was spread out with 35.6% under the age of 18, 11.5% from 18 to 24, 25.5% from 25 to 44, 16.8% from 45 to 64, and 10.6% who were 65 years of age or older. The median age was 27 years. For every 100 females there were 96.2 males. For every 100 females age 18 and over, there were 90.3 males.
The median income for a household in the city was $39,318, and the median income for a family was $41,223. Males had a median income of $32,154 versus $20,121 for females. The per capita income for the city was $13,921. About 7.9% of families and 9.6% of the population were below the poverty line, including 10.6% of those under age 18 and 2.0% of those age 65 or over.
Curt Brinkman Park features a skateboarding rink. Shelley High School, a building sometimes accused of looking like a potato celler, is in the background.
A gazebo on the greenbelt in Shelley, ID overlooks the Snake River as it flows over some rocks.