High Quality Content by WIKIPEDIA articles! Allegheny Islands State Park is a 43-acre (17 ha) Pennsylvania state park in Harmar Township, Allegheny County, Pennsylvania in the United States. The undeveloped park is composed of three alluvial islands located in the middle of the Allegheny River northeast of Pittsburgh. The islands are just north of the boroughs of Oakmont and Plum, and southwest of Cheswick. Bridges for the Pennsylvania Turnpike (Interstate 76) and the Bessemer and Lake Erie Railroad Branch of the Canadian National Railway cross the Allegheny River at the middle island.