Gwinnett County was created on December 15, 1818, and named for Button Gwinnett, one of the three Georgia signers of the Declaration of Independence. The county was formed from the combination of land that was ceded to the state of Georgia by the Cherokee and Creek Indians and a portion of Jackson County. Gwinnett was the 50th county to be organized in the state. The county currently covers 437 square miles and includes approximately 280,000 acres of land. This makes Gwinnett the 50th largest county in the state in landmass.

The home of Elisha Winn, near what is now Dacula, was the first Gwinnett County courthouse. Winn was also chosen to select the site for the first county seat and new courthouse. He paid $200 for a 250-acre lot in the center of the county. Early courthouse business was held in a log cabin until a more permanent structure was built in 1824. The City of Lawrenceville was incorporated and designated the county seat in 1821, when Gwinnett consisted of a cluster of agrarian communities. By 1850, Lawrenceville was a thriving metropolis with a census count of 11,257. A cotton mill was founded in 1851; Union troops burned it in 1864. In an 1871 fire, the courthouse was burned down, destroying most of the early records and deeds. A new courthouse, built on the square in Lawrenceville, was deemed inadequate after only 12 years, and was replaced by the building now known as the Historic Courthouse for $23,000 in 1885. It served as the center of Gwinnett government operations until 1988.

A railroad line, the Danville and Piedmont Air Line (now Norfolk Southern), was built through the county in 1871. The railroad induced the founding of new cities: Norcross, Duluth, Suwanee, and Buford. A spur line was run from Suwanee to Lawrenceville in 1881, and another main line, the Georgia, Carolina, and Northern Railroad (now CSX), was built in 1891 through Lilburn, Lawrenceville, and Dacula.

The county's first major industry came in 1868 when the RH Allen Tannery was established possibly at the Elisha Winn house that Robert Allen appears to have been renting before setting up in Buford. Brother Bona soon followed with the Bona Allen Tannery which later purchased the RH Allen Co. after Robert's death. Both tanneries made leather goods, harnesses, whips, shoes, and became famous for handmade saddles. During the Depression of the 1930s when a number of farms began to decline, the tannery employed 2,400. The 1940 Census recorded a county population of 29,087.

Gwinnett County moved into the modern era in 1950 when the U.S. Congress authorized the construction of Buford Dam to provide hydroelectric power, flood control, water supply, navigation, and recreational facilities.

The County constructed its major water and sewer main lines in the 1970s, which proved to be an essential step in preparing for the next decade. For three consecutive years, 1986 through 1988, Gwinnett ranked as the fastest growing county in the U.S. among counties with a population greater than 100,000. During that period, voters passed the 1986 bond issue, and the 1985 and 1988 one-percent special purpose local option sales tax programs, mechanisms which provided funds for significant capital investments. The late 1980s witnessed a dramatic increase in the County's road construction program, the development of a countywide Parks and Recreation program, construction of the Gwinnett Justice and Administration Center, renovation of the historic courthouse, construction of new public libraries, and other capital improvements.

Growth slowed during the recessions of 1990 and 2007, but the influx of new residents and businesses continued. The county's population in 2010 stood at 805,321, up more than 216,000 residents from the 2000 count of 588,448 (source: U.S. Census Bureau decennial population estimates). Gwinnett County's population is expected to reach one million residents by the year 2022.

Gwinnett has many advantages, beginning with its location and road system. The county is just 45 minutes from Hartsfield-Jackson Atlanta International Airport and 30 minutes from downtown Atlanta. Georgia Highway 316 has been extended to Athens, reducing travel time to the University of Georgia to 25 minutes. Gwinnett's infrastructure includes more than 2,750 miles of roadways to provide excellent mobility for our citizens.

According to the Georgia Department of Labor, 450,909 Gwinnett County residents were employed in 2020, and the unemployment rate was 6.3 percent.