Port Allen Harbor is located on the southern coast of Kauai. The project was authorized by the Rivers and Harbors Acts of 1935 and 1945. It was completed in 1948 at a cost of $1,837,513 (Federal: $1,637,513; non-Federal: $200,000).

The project consists of a 1,200-foot-long rubble mound breakwater on the east side of the bay; an entrance channel (500 feet wide and 35 feet deep); and a harbor basin (1,200 feet wide by 1,500 feet long, and 35 feet deep). The local sponsor is the State of Hawaii, Department of transportation. According to the latest waterborne commerce statistics, 4.3 million short tons of cargo was shipped through Port Allen Harbor in 2007.