The city has many preserved 19th-century era storefronts along its main street, some of which show distinct Chinese influences. Chinese began immigrating to Isleton around 1875, and at its peak, the Chinese population numbered approximately 1,500. A Chinese tong (community organization) building in Isleton was featured on a July 2008 episode of the PBS program History Detectives.
According to the United States Census Bureau, the city has a total area of 0.5 square miles (1.2 km²), of which, 0.4 square miles (1.0 km²) of it is land and 0.1 square miles (0.2 km²) of it (13.04%) is water.
As of the census of 2000, there were 828 people, 343 households, and 209 families residing in the city. The population density was 2,071.4 people per square mile (799.2/km²). There were 384 housing units at an average density of 960.6/sq mi (370.7/km²). The racial makeup of the city was 69.57% White, 1.45% African American, 1.45% Native American, 9.78% Asian, 0.24% Pacific Islander, 10.02% from other races, and 7.49% from two or more races. Hispanic or Latino of any race were 26.93% of the population.
There were 343 households out of which 29.7% had children under the age of 18 living with them, 39.9% were married couples living together, 14.9% had a female householder with no husband present, and 38.8% were non-families. 32.7% of all households were made up of individuals and 14.0% had someone living alone who was 65 years of age or older. The average household size was 2.41 and the average family size was 3.08.
In the city the population was spread out with 25.5% under the age of 18, 6.8% from 18 to 24, 27.1% from 25 to 44, 24.3% from 45 to 64, and 16.4% who were 65 years of age or older. The median age was 38 years. For every 100 females there were 102.4 males. For every 100 females age 18 and over, there were 103.6 males.
The median income for a household in the city was $33,958, and the median income for a family was $40,833. Males had a median income of $39,306 versus $22,500 for females. The per capita income for the city was $19,767. About 12.4% of families and 15.0% of the population were below the poverty line, including 25.0% of those under age 18 and 6.0% of those age 65 or over.
In the state legislature Isleton is located in the 5th Senate District, represented by Democrat Michael Machado, , and in the 15th Assembly District, represented by Republican Guy S. Houston. Federally, Isleton is located in California's 10th congressional district, which has a Cook PVI of D +9 and is represented by Democrat Ellen Tauscher.