The first people to call Polk County home arrived close to 12,000 years ago during the last ice age as the first paleo-indians arrived on the peninsula of Florida as they followed big game southward. By this time, the peninsula had gone through several expansions and contractions; at times the peninsula was much wider than it is today, while at other times it was almost entirely submerged with only a few small islands above sea level. These first paleo-indians were nomadic hunter/gatherers who did not establish any permanent settlers and they eventually gave way to the "archaic people" who were the ancestors of the Indians who came in contact with the Spaniards when they arrived on the peninsula. These Indians thrived on the peninsula and it is estimated that there were over 250,000 in 1492 when Columbus set sail for the New World. As was common elsewhere, the Indians' contact with Europeans had a devastating effect on the Indians. Small Pox, Measles and other diseases the Indians had no immunity for caused widespread epidemic and death. Those who had not succumbed to diseases such as Small Pox or Yellow Fever were either killed or enslaved. Eventually the remnants of these tribes would merge together with Creek Indians who arrived from the north and become the Seminole Indian tribe. Within a few hundred years, nearly the entire pre-columbian population of Polk County had been wiped out. The remnants of these Indians joined with renegade Creek Indians from Georgia and The Carolinas to form the Seminole Indian Tribe.
For around 250 years after Ponce De Leon arrived on the peninsula, the Spanish ruled Florida. In the late 17th century, Florida went through an unstable period in which the French and British ruled the peninsula. After the American Revolution, the peninsula briefly reverted back to Spanish rule. In 1819, Florida became a U.S. territory as a result of the Adams-Onis Treaty.
The county was established by the state government in 1861 on the eve of the American Civil War and named after former United States president James K. Polk. Polk County was formed by dividing Hillsborough County into eastern and western halves. The eastern half was named Polk, in honor of the 11th President of the United States, James Knox Polk. Polk was sworn in as president on the day after Florida's March 3, 1845 statehood; thus Polk was the earliest U.S. President to govern Florida as a state for a full presidential term.
Following the Civil War, the county commission established the county seat on 120 acres (0.49 km) donated in the central part of the county. Bartow, the county seat, was named after Francis S. Bartow, a confederate Colonel from Georgia who was the first confederate officer to die in battle during the first battle of the Civil War. Colonel Bartow was buried in Savannah, GA with military honors, and promoted posthumously to the rank of brigadier general. Fort Blount, as Bartow was then known, in a move to honor one of the first fallen heroes of the Confederacy, was one of several towns and counties in the South that changed their name to Bartow. The first courthouse built in Bartow was constructed in 1867. It was replaced twice, in 1884 and in 1908. As the third courthouse to stand on the site, the present structure houses the Polk County Historical Museum and Genealogical Library.
Growth in Polk County is driven by proximity to both the Tampa and Orlando metropolitan areas along the Interstate 4 corridor. Recent growth has been heaviest in Lakeland (closest to Tampa) and the Northeast areas near Haines City (nearest to Orlando). From 1990-2000, unincorporated areas grew 25%, while incorporated areas grew only 11%. In addition to developing cottage communities for commuters, there is evidence in Haines City of suburban sprawl into unincorporated areas. Despite the impressive growth rate, the unemployment rate of Polk has typically been higher than that of the entire state. In August 2010, the county had an unemployment rate of 13.4% compared to 11.7% for the entire state.
During the 2004 Atlantic hurricane season, three hurricanes, Charley, Frances and Jeanne all tracked over Polk County, intersecting in a triangle that includes the city of Bartow, Florida.
Winter Haven was best known as the home of Cypress Gardens, a theme park which closed Sept. 23, 2009. The city is now home to the theme park Legoland Florida, built on the site of Cypress Gardens. Country musician Gram Parsons was from a wealthy family in Winter Haven. Winter Haven was also home to the first Publix supermarket circa 1930 and Lakeland, Florida is where Publix's Corporate Offices are located. The town of Bartow was named in honor of Francis S. Bartow, the first Confederate officer to die in the American Civil War.