According to the United States Census Bureau, the city has a total area of 24.0 square miles (62.1 km²), of which, 23.9 square miles (62.0 km²) of it is land and 0.1 square miles (0.2 km²) of it (0.25%) is water. Stormwater surface runoff from the city drains to the Truckee River, a sensitive hydrological element because it empties into Pyramid Lake, which has no outlet and is the habitat of two endangered species.
There were 24,601 households out of which 35.2% had children under the age of 18 living with them, 50.0% were married couples living together, 12.0% had a female householder with no husband present, and 32.4% were non-families. 24.3% of all households were made up of individuals and 7.7% had someone living alone who was 65 years of age or older. The average household size was 2.67 and the average family size was 3.19.
In the city the population was spread out with 26.9% under the age of 18, 9.2% from 18 to 24, 31.6% from 25 to 44, 22.1% from 45 to 64, and 10.2% who were 65 years of age or older. The median age was 34 years. For every 100 females there were 97.7 males. For every 100 females age 18 and over, there were 96.0 males.
The median income for a household in the city was $45,745, and the median income for a family was $52,029. Males had a median income of $35,215 versus $28,242 for females. The per capita income for the city was $21,122. About 6.5% of families and 8.0% of the population were below the poverty line, including 9.8% of those under age 18 and 5.5% of those age 65 or over.
The population density in the area remained very low until 1904 when the Southern Pacific Railroad built a switch yard and maintenance sheds there. The city that sprung up around them was first called Harriman after Edward Harriman who was then president of the railroad. The city was quickly renamed Sparks after John Sparks, who was the Governor of Nevada at that time. This gesture was an unsuccessful attempt to forestall safety and tariff regulation of the railroads by the state.
Sparks remained a small and sleepy town until the 1950s, when economic growth in Reno triggered a housing boom in the area of Sparks north of the railroad. In the 1970s the area south of the railroad started to fill up with warehouses and light industry. In 1984 the tower for John Ascuaga's Nugget was finished, giving Sparks its first, and to this date only, high-rise casino. In 1996, the redevelopment effort of the old and unsightly B Street business district across from the Nugget that started in the early 1980s took a step forward with the opening of a multi-screen movie complex and the construction of a plaza area. This area, now known as Victorian Square, is a pedestrian-friendly district that hosts many open-air events.
Under direction of the U.S. Environmental Protection Agency, a comprehensive dynamic water quality computer model, the DSSAM Model was developed(Earth Metrics, 1987) to analyze impacts of a variety of land use and stormwater management decisions throughout the Truckee River Basin; this model was used to develop a set of surface runoff stormwater management measures for Sparks in the 1980s.