Horwich extends to and measures from north to south and west to east. The River Douglas flowing in a south westerly direction forms part of its northern boundary. The landscape to the north is dominated by Winter Hill, Rivington Pike and the West Pennine Moors. The highest point is on the moors in the north from where the ground slopes down towards the south and west, where the lowest land is about . On Wilders and Horwich Moors the underlying rock is Millstone Grit, and in the intermediate slopes are found the Lower Coal Measures of the Lancashire Coalfield. The Middle Coal Measures are found in the southwest of the township.