Situated on the southern shore of the Carquinez Strait, the population was 190 in 2020 according to the United States Census Bureau.

[6] Businessman George W. McNear built the Port Costa Warehouses and Dock Company west of the new ferry terminal in 1880.

[8][7] The Port Costa School, a classical revival building designed by architect William Wilde, was built in 1911, opened in 1912, and operated until 1966.

[10] For the early decades of Port Costa's existence, much of the town's commercial activities took place on wharves and docks along the waterfront.

These wharves and docks suffered from numerous fires between 1883 and 1941, and a large part of the "Waterfront Port Costa" area was demolished in 1921 after being badly damaged by shipworms.

[11] After California's wheat output dropped in the early 20th century and especially after the Southern Pacific (which took over the operations of the Central Pacific) constructed a railroad bridge at Martinez in 1930 to replace the ferry crossing, Port Costa lost population and importance.

Under this iteration, the warehouse housed multiple antique stores and, for two years, artist Clayton Bailey's Wonders of the World Museum.

[15][16] According to the United States Census Bureau, the CDP has a total area of 0.16 square miles (0.41 km2), all of it land.

Port Costa is surrounded by rolling hills grazed by cattle and managed by East Bay Regional Park District.

Carquinez Strait Regional Shoreline stretches from Crockett through Port Costa and to Martinez.