The A875 runs for 6.4 miles from Dumgoyne on the A81 to Kepculloch Toll on the A811, nominally cutting a corner off between these two roads – although the fact that the A875 passes through the villages of Killearn and Balfron means that the journey between the two end points can actually be made more quickly using the A81 and A811.
The route starts at a fork junction on the A81 in Strath Blane, 3½ miles north-west of the village of the same name. It climbs up the valley side, winding through trees and past open fields, to enter the village of Killearn after a mile or so. Zig-zagging through the village, with a sharp right hand bend near the church at the end of the main street, the road passes some very exclusive houses with some hidden away down side roads and long driveways. Just beyond the parish church, the B834 heads back west to the A81, while the A875 quickly leaves the village behind. After three quarters of a mile of winding through open country, the B818 forks right to Fintry and the Campsie Fells, while the A875 drops steadily down into the valley of the Endrick Water. Crossing the river by means of Endrick Bridge, the road enters Balfron, a textile-weaving village which was developed in the late 18th century.
The road climbs quite steeply at times through the village, passing a range of shops and negotiating a series of sharp bends in the oldest part of the settlement. On leaving Balfron, the road opens out and heads upwards over the hills in a series of ever longer straights, affording stunning views of the distant hills ahead. As the road improves, those distant hills emerge from the haze, changing from bluey-green to full colour. All too soon, however, this final stretch comes to an end as the A875 reaches the A811 at a T-junction at Kepculloch Toll.
The A875 is lined with mileposts, suggesting it has long been an important route; however, in 1922 it was not deemed important enough to be given a number. That didn't last long, however, and at some time in the mid to late 1920s the road, following the same route that it does today, was issued with the A875 number,.