Sidney was laid out in 1851 and was originally to be called Dayton. The survyeors were boarding with the Milton Richards family. Richards wife suggested they rename the city for her hometown, Sidney, Ohio.
The Sidney Iowa Championship Rodeo operated by American Legion Post No. 128 since 1924 claims to be the world's largest continuous outdoor rodeo and one of the world's largest rodeos with around 38,000 visitors each year. The event is held in late July/early August.
There were 491 households out of which 34.4% had children under the age of 18 living with them, 53.6% were married couples living together, 11.2% had a female householder with no husband present, and 32.6% were non-families. 28.9% of all households were made up of individuals and 18.3% had someone living alone who was 65 years of age or older. The average household size was 2.48 and the average family size was 3.05.
Population spread: 27.1% under the age of 18, 6.1% from 18 to 24, 24.2% from 25 to 44, 21.2% from 45 to 64, and 21.5% who were 65 years of age or older. The median age was 39 years. For every 100 females there were 87.9 males. For every 100 females age 18 and over, there were 78.9 males.
The median income for a household in the city was $36,375, and the median income for a family was $45,278. Males had a median income of $30,292 versus $24,135 for females. The per capita income for the city was $15,027. About 6.6% of families and 9.7% of the population were below the poverty line, including 12.2% of those under age 18 and 16.3% of those age 65 or over.