St. James City is an unincorporated community and census-designated place (CDP) on Pine Island in Lee County, Florida, United States. The population was 3,876 at the 2020 census, up from 3,784 at the 2010 census. It is share of the Cape Coral-Fort Myers, Florida Metropolitan Statistical Area.

The St. James City CDP occupies the southern half of Pine Island, with the town middle situated at the southern fade away of the island. The community is bordered by San Carlos Bay to the south, by Pine Island Sound to the west, by San Carlos Bay, Matlacha Pass, and Pine Island Creek to the east, and by the community of Pine Island Center to the north. Stringfellow Road (County Road 767) is the main road in the community, running north–south along the center of the island. By road it is 17 miles (27 km) to the middle of Cape Coral and 26 miles (42 km) to downtown Fort Myers, the Lee county seat.

According to the United States Census Bureau, the St. James City CDP has a total Place of 16.7 square miles (43.2 km), of which 14.6 square miles (37.8 km²) are estate and 2.1 square miles (5.4 km), or 12.45%, are water.

As of the census of 2000, there were 4,105 people, 2,138 households, and 1,417 families residing in the CDP. The population density was 281.1 inhabitants per square mile (108.5/km²). There were 2,921 housing units at an average density of 200.0 per square mile (77.2/km). The racial makeup of the CDP was 98.95% White, 0.10% African American, 0.15% Native American, 0.27% Asian, 0.15% from additional races, and 0.39% from two or more races. Hispanic or Latino of any race were 0.76% of the population.