The county derives its name from the Merced River, or El Río de Nuestra Señora de la Merced (River of Our Lady of Mercy), named in 1806 by an expedition headed by Gabriel Moraga, which came upon it at the end of a hot dusty ride on the El Camino Viejo across the San Joaquin Valley in Spanish colonial Las Californias Province.

Between 1841 and 1844, during the period when Alta California was a territory of independent Mexico, four Mexican land grants were made in what became Merced County: Rancho Orestimba y Las Garzas, Rancho Panoche de San Juan y Los Carrisolitos, Rancho San Luis Gonzaga, and Rancho Sanjon de Santa Rita Merced County was formed in 1855 from parts of Mariposa County.

55.1% spoke English, 35.3% Spanish, 3.2% Hmong, 2.9% Portuguese and 1.0% Punjabi as their first language.

As of 2008, according to the Lao Family Community, a nonprofit organization, about 8,000 Hmong lived in Merced County.

The Board consists of five members, elected by districts, who serve four-year staggered terms.

[28] In the California State Legislature, Merced County is in the 27th Assembly District, represented by Democrat Esmeralda Soria, and the 14th Senate District, represented by Democrat Anna Caballero.

According to the California Secretary of State, as of October 20, 2008, there were 97,179 registered voters in Merced County.

Atwater and the county's unincorporated areas have Republican plurality registration advantages.

All of the other cities and towns in the county have Democratic pluralities or majorities in voter registration.

The following table includes the number of incidents reported and the rate per 1,000 persons for each type of offense.

According to America's Labor Market Information System 2014 report,[36] the companies with the largest employment in Merced are, in alphabetical order: Merced County grows 90% of California's sweet potato crop,[37] due in part to the efforts of John Buttencourt Avila, called "the father of the sweet potato industry".

The population ranking of the following table is based on the 2010 census of Merced County.