Loudoun is a parish in East Ayrshire, Scotland and lies between five and ten miles east of Kilmarnock. The parish roughly encompasses the northern half of the Upper-Irvine Valley and borders Galston Parish at the River Irvine.

The River Irvine is a river that flows through southwest Scotland. Its watershed is on the Lanarkshire border of Ayrshire at an altitude of 810 feet (250 m) above sea-level, near Loudoun Hill, Drumclog, and 7 miles SW by W of Strathaven. It flows 29+1⁄2 mi (47.5 km) westward, dividing the old district of Cunninghame from that of Kyle, until it reaches the sea via Irvine Harbour in the form of the Firth of Clyde, and flows into Irvine Bay by the town of Irvine. It has many tributaries, some of which form parish, district and other boundaries.