Glassport is a borough in Allegheny County, Pennsylvania, United States, approximately 10 miles (16 km) south of Pittsburgh and the confluence of the Monongahela and Allegheny rivers where they form the Ohio River. Glassport lies along the east side of the Monongahela river in the "Mon valley", where many blue-collar municipalities have suffered severe economic decline in the wake of the loss of steel-making throughout the Greater Pittsburgh Area. In 1910, the population of Glassport was 5,540. By 1940, it had risen to 8,748, but has since declined to 4,993 as of the 2000 census.