It was located near the base of the Harmony Peninsula, where the Tilapia River runs into Tranquility Bay. It had a large downtown business district, factories and warehouses along the river banks a little ways upstream, and large residential neighborhoods in between. There was also a double row of hotels and condo towers running along the shoreline either side of the downtown area, and beautiful white-sand beaches in front of them.
Port Prosperity was founded in 2210 by Harrington Industries to be the capital of their newly-reestablished colony, after the previous human colonization effort was destroyed by a Bug invasion in 2194. When the Earth Federation invaded the planet in early 2265, the city was heavily fought over and suffered extreme damage. When the local Duke refused to surrender under threat of orbital bombardment, Joseph Smythe ordered the EFS Poseidon to fire a singularity into Tranquility Bay with its Gravitic Ram. The resulting mile-high tsunami obliterated the city and wiped it off the map. The planetary capital was moved to Foxburg on the opposite coast.