From Wikipedia:
Although most historians count 87 members of the party, Stephen McCurdy in the Western Journal of Medicine includes Sarah Keyes?Margret Reed's mother?and Luis and Salvador, bringing the number to 90. Five people had already died before the party reached Truckee Lake: one from tuberculosis (Halloran), three from trauma (Snyder, Wolfinger and Pike), and one from exposure (Hardkoop). A further 34 died between December 1846 and April 1847: 25 males and 9 females.