Thornburg is a borough in Allegheny County in the U.S. state of Pennsylvania.

[4] According to the United States Census Bureau, the borough has a total area of 0.4 square miles (1.0 km2), all land.

None of the families and 1.3% of the population were living below the poverty line, including no under eighteens and none of those over 64.

Thornburg has borders with Robinson Township to the north and west and Rosslyn Farms to the southwest.

Across Chartiers Creek to the south and east, Thornburg runs adjacent with Crafton.