As of the census^GR2 of 2000, there were 108,724 people, 39,206 households, and 22,778 families residing in the city. The population density was 2,685.8/km² (6,956.3/mi²). There were 40,406 housing units at an average density of 998.1/km² (2,585.2/mi²).

Three freeways serve Costa Mesa including the :California State Highway 73 and California State Highway 55 (also known as the Costa Mesa Freeway) and the San Diego Freeway, Interstate 405.

28.1% of all households were made up of individuals and 6.3% had someone living alone who was 65 years of age or older. The average household size was 2.69 and the average family size was 3.34.There were 39,206 households out of which 29.2% had children under the age of 18 living with them, 42.8% were married couples living together, 10.3% had a female householder with no husband present, and 41.9% were non-families.

Institutions of higher learning located in Costa Mesa include Orange Coast College, a pioneer in the community college concept, a private institution Vanguard University, affiliated with the Assemblies of God and Whittier Law School, a satellite of Whittier College.

The median income for a household in the city was $50,732, and the median income for a family was $55,456. Males had a median income of $38,670 versus $32,365 for females. The per capita income for the city was $23,342. About 8.2% of families and 12.6% of the population were below the poverty line, including 16.0% of those under age 18 and 6.2% of those age 65 or over.

Costa Mesa's local economy relies heavily on retail and services. The single largest center of commercial activity is South Coast Plaza, a  retail center noted for its architecture and size. The volume of sales generated by South Coast Plaza, on the strength of 322 stores, places it among the highest volume regional shopping centers in the nation. It generates more than one billion dollars per year. Costa Mesa is also known for its excess of car dealerships and pet supply stores. Some manufacturing activity also takes place in the city, mostly in the industrial, southwestern quarter, which is home to a number of electronics, pharmaceuticals and plastics firms.

Costa Mesa recreation:

Costa Mesa offers 26 parks, a municipal golf course, 26 public schools and 2 libraries. It is also home to the Orange County Fairgrounds, which hosts one of the largest fairs in California, the Orange County Fair, each July. The Fair receives more than one million visitors each year. The Fair also has the Pacific Amphitheater which is adjacent to it.