The policies of Buchanan Castle are situated some 17 miles (27.5km) to the north- west of Glasgow between the village of Drymen and the east shore of Loch Lomond. They are enclosed to the north by the B837, to the south by the River Endrick and to the east by the A809. The River Endrick forms the boundary between Strathclyde and Central Region. The parkland is set on the flat floodplain of the river. Soil conditions are sandy and have been conducive to the uses made of the park since its original layout. The parkland of Kilmaronock Castle to the south of the river is particularly significant from the Park of Buchanan. To the north the hills rise towards Ben Lomond 3,194', (974m) eastwards to the Campsie Fells, south to the Kilpatrick Hills and west to the hills by Loch Lomond and Loch Long. Magnificent views of these hills and mountains are gained from Buchanan. The Castle, its woodlands and parkland are highly significant from the A811 to the south. From the A837 in the north, the woodlands screen the designed landscape which they enclose.
Buchanan Castle is situated on elevated ground overlooking the extensive parkland which stretches for approximately 2.5km along the banks of the River Endrick, the southern boundary of the policies. Woodlands extend along the northern boundary of the B837 and project into the estate, forming enclosures to the former parklands lying north of the Castle. Buchanan Old House, now converted as the Golf Clubhouse, is situated on the edge of the parkland to the north-west of the Castle. Documentary map evidence is provided by a design plan by Wm. Adam of 1745 (SRO RHP 6150), General Roy's map of c.1750, the 1st edition OS map of 1871, and the 2nd edition OS map of c.1910.
Reference to the design plan by William Adam, and General Roy's map, indicates that the 18th century designed landscape was confined to the north of the river. Comparison of the 1st edition OS map of 1871 with these earlier records shows that the policies were extended to the east and south in the intervening period. By 1871 a drive, extending across the River Endrick and continuing down a beech avenue to Gargowan Lodge on the A811, had been added and was in use until recent years. The parkland to the south of the river, part of Kilmaronock House policies, is not thought to have ever been part of Buchanan but is, however, highly significant from within its policies. Views to the surrounding hills are important from within the site. William Adam's design of 1745 envisaged avenues radiating to the west from the Old House of Buchanan. The vista down the principal avenue was centred on the island of Inchmurrin in Loch Lomond where the Duke of Montrose had built a pleasure lodge beside the existing ruined Castle. This plan, however, does not appear to have been carried out as, according to Pennant in his description of c.1770, the planned view was not visible from the Castle. There is no view of Loch Lomond today from within the policies, due to the flat nature of the landscape. The designed landscape today includes some 1,661 acres (672ha).