Tampa/tmp/ is a city in the U.S. state of Florida. It serves as the county seat for Hillsborough County and is located on the west coast of Florida, on Tampa Bay near the Gulf of Mexico. The population of Tampa in 2011 was 346,037. The current location of Tampa was once inhabited by indigenous peoples of the Safety Harbor culture, most notably the Tocobaga and the Pohoy, who lived along the shores of Tampa Bay. It was briefly explored by Spanish explorers in the early 16th century, but there were no permanent American or European settlements within today's city limits until after the United States had acquired Florida from Spain in 1819. In 1824, the United States Army established a frontier outpost called Fort Brooke at the mouth of the Hillsborough River, near the site of today's Tampa Convention Center. The first civilian residents were pioneers who settled near the fort for protection from the nearby Seminole population. The town grew slowly until the 1880s, when railroad links, the discovery of phosphate, and the arrival of the cigar industry jump-started its development and helped it to grow into an important city by the early 1900s. Today, Tampa is a part of the metropolitan area most commonly referred to as the Tampa Bay Area. For U.S. Census purposes, Tampa is part of the Tampa-St. Petersburg-Clearwater, Florida Metropolitan Statistical Area. The four-county area is composed of roughly 2.9 million residents, making it the second largest metropolitan statistical area (MSA) in the state, and the fourth largest in the Southeastern United States, behind Miami, Washington, D.C. and Atlanta. The Greater Tampa Bay area has over 4 million residents and generally includes the Tampa and Sarasota metro areas. The Tampa Bay Partnership and U.S. Census data showed an average annual growth of 2.47 percent, or a gain of approximately 97,000 residents per year. Between 2000 and 2006, the Greater Tampa Bay Market experienced a combined growth rate of 14.8 percent, growing from 3.4 million to 3.9 million and hitting the 4 million population mark on April 1, 2007. A 2012 estimate shows the Tampa Bay area population to have 4,310,524 people and a 2017 projection of 4,536,854 people.