The Little Platte is dammed just east of the city to form the Smithville Reservoir.

[7] Smithville is named after Humphrey "Yankee" Smith (1774 – May 5, 1857) after he settled at the site in 1822.

[9] The town was originally known as "Smith's Mill" but ultimately became "Smithville" as it was easier to pronounce.

[11][12] The 2020 United States census[14] counted 10,406 people, 3,647 households, and 2,864 families in Smithville.

There were 3,761 housing units at an average density of 232.7 per square mile (89.9/km2).

Of all households, 16.7% consisted of individuals and 8.4% had someone living alone who was 65 years of age or older.

As of the census[16] of 2010, there were 8,425 people, 3,115 households, and 2,321 families living in the city.

There were 3,280 housing units at an average density of 210.8 per square mile (81.4/km2).

21.9% of all households were made up of individuals, and 8.4% had someone living alone who was 65 years of age or older.

There were 2,220 housing units at an average density of 161.9 per square mile (62.5/km2).

22.4% of all households were made up of individuals, and 8.6% had someone living alone who was 65 years of age or older.