As of the census of 2000, there were 140,030 people, 44,804 households, and 31,945 families residing in the city. The population density was 1,219.6/km² (3,158.6/mi²). There were 45,922 housing units at an average density of 400.0/km² (1,035.8/mi²). The racial makeup of the city was 43% White, 11% Black or African American, 0.84% Native American, 19% Asian, 1.91% Pacific Islander, 16.81% from other races, and 7.52% from two or more races. 34.17% of the population were Hispanic or Latino of any race.
There were 44,804 households out of which 37.0% had children under the age of 18 living with them, 50.3% were married couples living together, 14.5% had a female householder with no husband present, and 28.7% were non-families. 20.9% of all households were made up of individuals and 7.3% had someone living alone who was 65 years of age or older. The average household size was 3.08 and the average family size was 3.58.
In the city the population was spread out with 26.8% under the age of 18, 10.9% from 18 to 24, 33.4% from 25 to 44, 18.8% from 45 to 64, and 10.2% who were 65 years of age or older. The median age was 32 years. For every 100 females there were 98.5 males. For every 100 females age 18 and over, there were 96.3 males.
The median income for a household in the city was $51,177, and the median income for a family was $54,712. Males had a median income of $37,711 versus $31,481 for females. The per capita income for the city was $19,695. About 7.2% of families and 10.0% of the population were below the poverty line, including 11.7% of those under age 18 and 7.2% of those age 65 or over.
Hayward is served by Interstate 880 (Nimitz Freeway) and Interstate 238. Interstate 580 is just north of the city. It is also served by State Route 92 (Jackson Street) and State Route 238 (Mission Boulevard/Foothill Boulevard). Mission Boulevard has been long known for chronic traffic congestion because of the lack of a freeway alternative to I-880; past proposals to convert Mission Boulevard to a freeway or build the 238 bypass have been controversial. Mission, Jackson and Foothill all converge into one congested intersection south of downtown locally known as "Five Flags", and there has been talk of building an overpass to alleviate traffic. Otherwise, due to congestion in the immediate downtown area affecting local businesses, a new plan on the books is to convert A Street, Mission and Foothill to one-way thoroughfares counterclockwise.
BART has two stations in Hayward: Hayward, in the downtown district; and South Hayward, near the Hayward-Union City border. The AC Transit bus system also serves the Hayward community. Amtrak, the national rail passenger system, provides daily service at Hayward with the Capitol Corridor, which runs between San Jose and Auburn.