Canonsburg is a borough in Washington County, Pennsylvania, 18 miles (29 km) southwest of Pittsburgh. Canonsburg was laid out by Colonel John Canon in 1789 and incorporated in 1802.
The borough is in a rich coal district, and most of the town's work force once worked in local steel mills or coal mines. Canonsburg's population in 1910, including South Canonsburg, which was annexed in 1911, was 5,588; in 1920 it was 10,632; and in 1940 it was 12,599. The population was 8,992 at the 2010 census.
Interstate 79 and Route 19 pass through the town, as do several railroad lines. The active railroad system in Canonsburg is now The Pittsburgh and Ohio Central Railroad. A trolley used to operate from Washington, Pennsylvania to Pittsburgh through Canonsburg until 1953.