Best Answer: The biggest city in Gwinnett is Lawrenceville with a population of 28,393 (2005 estimation) the city has a total area of 13.1 square miles (33.8 km) Lawrenceville is the biggest city in Gwinnett County. There are several cities in Gwinnett County, GA Lawrenceville is the County seat, there is Suwannee which was recently voted one of the top 10 cities in the US to live also: Lilburn Norcross Duluth Auburn Dacula Sugar Hill and more.