Big Pine Key is a census-designated place and unincorporated community located in Monroe County, Florida, within the United States. It sits on an island of the same name in the Florida Keys, positioned between nearby islands such as Upper Sugarloaf Key, Cudjoe Key, and Bahia Honda Key. The community serves as a significant residential and tourist hub in this archipelago, characterized by its unique geological foundation of limestone rock interfaces that support rare ecosystems.

The island's development was heavily influenced by the Overseas Railroad, with Big Pine Key serving as the location for one of its stations. This infrastructure was supported by local resources, including an abandoned rock quarry known as the Blue Hole, which provided material for road fills and railroad construction. The area has since transitioned into a protected environment, with much of the island designated as part of the National Key Deer Refuge to preserve the habitat of the endangered Key deer subspecies.

The community is bisected east to west by U.S. Route 1, also known as the Overseas Highway, which orients north-south along the key's eastern edge at mile markers 29.5 to 33. Notable landmarks include the Blue Hole, a freshwater-filled quarry hosting wildlife like alligators and iguanas, and the National Key Deer Refuge visitor center. The island features a shopping plaza with a Winn-Dixie grocery store and various retail outlets, alongside residential areas connected by Key Deer Boulevard and smaller roads.

Visitor appeal centers on the opportunity to observe the Key deer, the smallest subspecies of white-tailed deer, which are endemic to the area between Big Pine Key and Sugarloaf Key. The island offers activities such as fishing, kayaking, and snorkeling, with access to nearby Looe Key reefs. The presence of feral chickens in shopping plazas and the proximity to Bahia Honda State Park enhance its recreational profile, while strict speed limits and fencing along U.S. 1 protect wildlife from traffic.

As of the 2020 census, Big Pine Key had a population of 4,521 residents living in 2,099 households. The local economy relies on tourism, retail, and services, with accommodation limited to RV camping and motel-style units. Access is restricted to U.S. Route 1 by road or by sea, as there is no airport on the island; the nearest facilities are in Marathon or on nearby Sugarloaf Key. The area's freshwater lens supports diverse plant life, including Caribbean Slash Pine, which defines the local landscape.