Derby is a city in Lucas County, Iowa, United States.

[4] According to the United States Census Bureau, the city has a total area of 0.26 square miles (0.67 km2), all land.

There were 43 housing units at an average density of 168.4 per square mile (65.0/km2).

There were 55 housing units at an average density of 211.5 per square mile (81.7/km2).

25.5% of all households were made up of individuals, and 10.7% had someone living alone who was 65 years of age or older.

There were 63 housing units at an average density of 239.3 per square mile (92.4/km2).

34.0% of all households were made up of individuals, and 18.9% had someone living alone who was 65 years of age or older.

There were 6.1% of families and 4.5% of the population living below the poverty line, including no under eighteens and 9.5% of those over 64.