Galveston County History dates back as early as 10,000 B.P. Evidence suggests that some Indian groups lived in the area and that exploitation of marine resources on the coastal margin occurred during the Late Prehistoric period. Bone-tempered pottery from this time has been excavated at campsites in the Galveston Bay area.

Sixteenth-century Spanish explorers knew Galveston Island as Isla de Malhado, the "Isle of Misfortune," or Isla de Culebras, the "Isle of Snakes." Juan de Grijalva discovered the island in 1519. In 1783 José Antonio de Evia,qv a Spanish navigator, surveyed the channel and named the bay Galvezton for Viceroy Bernardo de Gálvez,qv who befriended the United States in the Revolutionary War.

American presence in Galveston County began in 1815 when Henry Perry and Warren D. C. Hall,qqv former members of the Gutiérrez-Magee expedition,qv landed at Bolivar Point in September with three ships and 200 men. Perry named the point for Simón Bolívar, the "Liberator," who commissioned him to attack Spanish commerce on the Gulf and direct expeditions against the Spanish in Mexico. By 1817 a thousand inhabitants populated the island. The period from 1815 to 1821, however, was dominated by freebooters, filibusters, and pirates, notably the Frenchmen Louis Michel Aury and Jean Laffite.

Galveston County was formed in 1838 under the republic from Harrisburg, Liberty, and Brazoria counties and organized in 1839. The county was organized in 1839. By 1839 steamers that furnished supplies to much of Texas plied the distance between the port and New Orleans, and construction of the Galveston wharvesqv began in that year. The antebellum port shipped cotton and cottonseed oil, with less important quantities of sugar, molasses, cattle, hides, and pecans, while Galveston finance and commission businesses supported the region's agriculture and commerce. In the 1840s and 1850s large numbers of immigrants began to arrive at the port fleeing the revolutions in Europe.

With the onset of the Great Depression,qv Galveston began a decline in relation to other Texas cities that lasted until the 1970s. Though few Galveston County banks failed, cotton firms rapidly departed for Houston, and manufacturing firms dwindled from 305 in 1900 to only ninety-seven in 1930. After the war, the city of Galveston purchased the port's existing facilities, which had been privately owned since their founding in 1854, and began to modernize. Elsewhere in the county, prosperity increased as eight oilfields with 272 oil wells produced more than 4.6 million barrels of oil by 1944.

In the 1970s preservation efforts were made to reclaim historical landmarks in Galveston, including the Strand,qv once known as the "Wall Street of the South." Texas A&M College of Marine Science and Maritime Research opened at Galveston, developers built shopping malls, and revitalization began. Politically, Galveston County residents have voted consistently for Democratic candidates, with few exceptions. Republican candidates won a majority in 1896 (William McKinley), 1956 (Dwight D. Eisenhowerqv), 1972 (Richard M. Nixon), and 1984 (Ronald Reagan). In 1982, 98,887 registered voters lived in the county.