Middlebrook is a locality that spans the boundaries of Horwich and Lostock in the Metropolitan Borough of Bolton, Greater Manchester, England (historically a part of Lancashire). The name Middlebrook is derived from the watercourse the Middle Brook which starts at Red Moss, the mossland south of Horwich. Further downstream the Middle Brook joins with other tributaries and becomes the River Croal which runs through Bolton and eventually joins the River Irwell at Kearsley.