This was an intermediate signal box between Dalry Junction and Dalgarven Signal Box. The box was on the west side of the line just north of the bridge over the Dusk Water and with Monkcastle itself to the west over the River Garnock.
The railway was prepared for quadrupling with space for an additional two lines on the west side, but these were not opened.
The box closed in 1942. The line remains open as a double track electrified line.