Declo is a city in Cassia County, Idaho, United States. It is part of the Burley, Idaho micropolitan area. The population was 343 at the time of the 2010 census, up from 338 in 2000. History The city was originally named Marshfield. In 1916, the name was changed to Declo. The Central Post Office told the community to choose another name not to exceed five letters. the last initials of the first five men to enter the post office were recorded: August Detlef, George Eldredge, Hyrum Lewis, James Cooley, and Carl Osterhout. The Central Post Office said they preferred Declo instead of Delco, and such it was named. The J. R. Simplot Company was founded in 1923 near Declo by 14-year-old entrepreneur J. R. Simplot, who had moved to the area with his family as a toddler. The corporate headquarters for the company are now located in Boise. Geography Declo is located at (42.519441, -113.629978), at an elevation of above sea level. According to the United States Census Bureau, the city has a total area of , all of it land. The Hillside Letter "D" can be seen in the southeast () Climate According to the Köppen Climate Classification system, Declo has a semi-arid climate, abbreviated "BSk" on climate maps. Demographics 2010 census As of the census of 2010, there were 343 people, 115 households, and 87 families residing in the city. The population density was . There were 127 housing units at an average density of . The racial makeup of the city was 85.1% White, 4.1% Native American, 9.9% from other races, and 0.9% from two or more races. Hispanic or Latino of any race were 15.2% of the population. There were 115 households, of which 45.2% had children under the age of 18 living with them, 51.3% were married couples living together, 15.7% had a female householder with no husband present, 8.7% had a male householder with no wife present, and 24.3% were non-families. 21.7% of all households were made up of individuals, and 9.6% had someone living alone who was 65 years of age or older. The average household size was 2.98 and the average family size was 3.44. The median age in the city was 29.8 years. 35.6% of residents were under the age of 18; 8.7% were between the ages of 18 and 24; 22.3% were from 25 to 44; 22.4% were from 45