St. Johns Countys history begins in 1821, when Colonel Robert Butler received Spanish East Florida from Captain-General Colonel Jos M. Coppinger. Butler represented Major General Andrew Jackson, federal military commissioner for the Florida provinces (las Floridas) with the powers of governor, exercising the powers of the Captain General and the Intendants of the Island of Cuba and the Governors of the said provinces, respectively, who ordained that all of that country lying east of the river Suwannee should be designated as the County of St. Johns.
St. Johns was established, along with Escambia County (in the former West Florida province), on July 21, 1821, just eleven days after Butler received Florida for the United States, and only five days from the date that the city of St. Augustine was incorporated.
The name Saint John's was derived from the Spanish mission (c. 1580) San Juan del Puerto or Saint John of the Harbor. The apostrophe was dropped in 1932 by the U.S. Department of the Interior because an apostrophe implied ownership.
It was a huge county, encompassing most of peninsular Florida, or more than 39,000 square miles; it was 475 miles long by 165 miles wide. Much of the land was uninhabited. Saint Augustine (1565) was the oldest permanent European settlement, and there were Native Americans in the county as well.
As of the census of 2000, there were 123,135 people, 49,614 households, and 34,084 families residing in the county. The population density was 202 people per square mile (78/km). There were 58,008 housing units at an average density of 95 per square mile (37/km). The racial makeup of the county was 90.92% White, 6.29% African American, 0.26% American Indian, 0.95% Asian, 0.05% Pacific Islander, 0.55% from other races, and 0.97% from two or more races. Hispanic or Latino of any race were 14.8% of the population. There is a Jewish community.
There were 49,614 households out of which 29.20% had children under the age of 18 living with them, 56.80% were married couples living together, 8.90% had a female householder with no husband present, and 31.30% were non-families. 24.30% of all households were made up of individuals and 9.40% had someone living alone who was 65 years of age or older. The average household size was 2.44 and the average family size was 2.90.
The age of the population was spread out with 23.10% under the age of 18, 7.00% from 18 to 24, 27.60% from 25 to 44, 26.40% from 45 to 64, and 15.90% who were 65 years of age or older. The median age was 41 years. For every 100 females there were 94.50 males. For every 100 females age 18 and over, there were 91.50 males.
The median income for a household in the county was $50,099, and the median income for a family was $59,153. Males had a median income of $40,783 versus $27,240 for females. The per capita income for the county was $28,674. About 5.10% of families and 8.00% of the population were below the poverty line, including 9.30% of those under age 18 and 6.20% of those age 65 or over.