Declo is a city in Cassia County, Idaho, United States.

[6] 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.

According to the United States Census Bureau, the city has a total area of 0.28 square miles (0.73 km2), all of it land.

There were 127 housing units at an average density of 453.6 per square mile (175.1/km2).

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.

10.7% of all households were made up of individuals, and 2.9% had someone living alone who was 65 years of age or older.