The parish lies on the neck of land in Argyll & Bute between Loch Long and the freshwater Loch Lomond. From a starting point at the middle of Loch Long opposite the entrance to Glen Douglas, the parish boundary goes straight through the middle of that glen to meet the county boundary on Loch Lomond side; it continues northwards following that boundary on the A82 on the east side of Loch Lomond to the road bridge over the River Falloch, where it turns west along the county boundary until it meets the Loin Water. At that point the ecclesiastical parish continues in a straight line to the top of the "Rest-and-be-Thankful" on the A83, then south-east in a straight line to Loch Long at Coilessan Farm, whence it continues south down Loch Long to the point opposite Glen Douglas.