Diagonal is a city in northwest Ringgold County, Iowa, the United States.

[3] The community was named for the fact that two railroads intersected diagonally near the town site.

The Grand River flows past the east side of the town.

[5] According to the United States Census Bureau, the city has a total area of 0.90 square miles (2.33 km2), all land.

There were 145 housing units at an average density of 161.1 per square mile (62.2/km2).

37.0% of all households were made up of individuals, and 17.6% had someone living alone who was 65 years of age or older.

There were 154 housing units at an average density of 169.6 per square mile (65.5/km2).

31.7% of all households were made up of individuals, and 16.5% had someone living alone who was 65 years of age or older.