Port St. John is a census-designated place located in Brevard County, Florida, United States. It is situated on the east coast of the state, approximately midway between Titusville and Cocoa. The population was 10,103 at the 2010 census.

Port St. John is a residential community with many amenities for its residents. The area has several parks and recreational areas including Port St. John Community Park, which features a playground, basketball court, picnic pavilion and walking trails. There are also several shopping centers in the area including Space Coast Plaza and Port St. John Shopping Center.

The area is served by Brevard Public Schools and there are several elementary schools in the area including Challenger 7 Elementary School, Endeavour Elementary School and Discovery Elementary School. There are also two middle schools – Space Coast Junior/Senior High School and Kennedy Middle School – as well as one high school – Astronaut High School.

Port St. John is home to many local businesses including restaurants, banks, grocery stores and other retail outlets. The area also has a number of medical facilities including Parrish Medical Center and Health First Cape Canaveral Hospital.

The climate in Port St. John is subtropical with hot summers and mild winters with temperatures rarely dropping below freezing point during winter months. The average annual temperature is around 73°F (23°C). The area receives an average of 54 inches (137 cm) of rain per year with most of it falling during summer months from June to September when thunderstorms are common occurrences due to the warm temperatures and high humidity levels in the air during this time of year.