As of the census of 2000, there were 4,659 people, 1,945 households, and 1,229 families residing in the city. The population density was 798.2 people per square mile (308.0/km²). There were 2,118 housing units at an average density of 362.9/sq mi (140.0/km²). The racial makeup of the city was 95.73% White, 0.11% African American, 0.19% Native American, 0.58% Asian, 0.06% Pacific Islander, 2.75% from other races, and 0.58% from two or more races. Hispanic or Latino of any race were 6.25% of the population.
There were 1,945 households out of which 29.8% had children under the age of 18 living with them, 49.7% were married couples living together, 10.1% had a female householder with no husband present, and 36.8% were non-families. 31.7% of all households were made up of individuals and 17.4% had someone living alone who was 65 years of age or older. The average household size was 2.36 and the average family size was 2.98.
In the city the population was spread out with 25.6% under the age of 18, 8.5% from 18 to 24, 25.6% from 25 to 44, 21.4% from 45 to 64, and 18.8% who were 65 years of age or older. The median age was 38 years. For every 100 females there were 89.9 males. For every 100 females age 18 and over, there were 85.1 males.
The median income for a household in the city was $32,701, and the median income for a family was $45,263. Males had a median income of $31,674 versus $21,684 for females. The per capita income for the city was $17,244. About 5.2% of families and 7.6% of the population were below the poverty line, including 13.3% of those under age 18 and 7.7% of those age 65 or over.
Amtrak, the national passenger rail system, provides service to Osceola, operating its California Zephyr daily in both directions between Chicago, Illinois, and Emeryville, California, across the bay from San Francisco. A bus connection is available from Osceola to Des Moines.