Martha Cox (1844-1898) was an American ranch hand who worked at MacFarlane's Ranch in Girvin, Pecos County, Texas during the 1890s. In 1898, her son Jimmy Cox borrowed Drew MacFarlane's wagon to take Martha to a doctor, but they were ambushed and murdered by the Del Lobo Gang while riding through outlaw country at Brittlebrush Trawl in Hennigan's Stead. The Arizona Kid later discovered their bodies while searching for the stolen wagon at the behest of Bonnie MacFarlane.