According to the International Union for Conservation of Nature (IUCN), 65 mammal species in the United States are threatened or nearly threatened with extinction.^[1] The IUCN has classified each of these species into one of four conservation statuses: near threatened NT, vulnerable VU, endangered EN, and critically endangered CR. Also included in the list are 5 species that became extinct EX since the 1500s.

Family Balaenidae (bowhead and right whales)

• North Atlantic right whale (Eubalaena glacialis) CR ^IUCN
• North Pacific right whale (Eubalaena japonica) EN ^IUCN
  • Northeast Pacific subpopulation CR ^IUCN

Family Balaenopteridae (rorquals)

• Sei whale (Balaenoptera borealis) EN ^IUCN
• Blue whale (Balaenoptera musculus) EN ^IUCN
• Fin whale (Balaenoptera physalus) VU ^IUCN
• Humpback whale (Megaptera novaeangliae) LC ^IUCN
  • Oceania subpopulation EN ^IUCN

Family Bovidae (bovids)

• Aoudad (Ammotragus lervia) VU ^IUCN (introduced from North Africa)
• Blackbuck (Antilope cervicapra) LC ^IUCN (introduced from India)
• American bison (Bison bison) NT ^IUCN

Family Cervidae (deer)

• Hog deer (Axis porcinus) EN ^IUCN (introduced from South Asia)
• Reindeer (Rangifer tarandus) VU ^IUCN
• Philippine deer (Rusa marianna) VU ^IUCN (introduced from Philippines)
• Sambar deer (Rusa unicolor) VU ^IUCN (introduced from South Asia)

Family Monodontidae (narwhal and beluga whale)

• Beluga whale (Delphinapterus leucas) LC ^IUCN
  • Cook Inlet subpopulation CR ^IUCN
• Narwhal (Monodon monoceros) LC ^IUCN (Occasional vagrant from Arctic Ocean north of Canada, Greenland, and Russia)

Family Physeteridae (sperm whale)

• Sperm whale (Physeter macrocephalus) VU ^IUCN

Family Canidae (canids)

• Red wolf (Canis rufus) CR ^IUCN
• Island fox (Urocyon littoralis) NT ^IUCN

Family Felidae (cats)

• Jaguar (Panthera onca) NT ^IUCN

Family Mephitidae (skunks)

• Eastern spotted skunk (Spilogale putorius) VU ^IUCN

Family Mustelidae (mustelids)

• Sea otter (Enhydra lutris) EN ^IUCN
• Black-footed ferret (Mustela nigripes) EN ^IUCN
• Sea mink (Neogale macrodon) EX ^IUCN since 1860s

Family Odobenidae (walrus)

• Walrus (Odobenus rosmarus) VU ^IUCN

Family Otariidae (eared seals)

• Northern fur seal (Callorhinus ursinus) VU ^IUCN
• Steller sea lion (Eumetopias jubatus) NT ^IUCN
  • Western Steller sea lion (E. j. jubatus) EN ^IUCN

Family Phocidae (earless seals)

• Hooded seal (Cystophora cristata) VU ^IUCN (Occasional vagrant from Canada, Greenland, and Norway)
• Hawaiian monk seal (Neomonachus schauinslandi) EN ^IUCN
• Caribbean monk seal (Neomonachus tropicalis) EX ^IUCN since 1950s

Family Ursidae (bears)

• Polar bear (Ursus maritimus) VU ^IUCN

Family Emballonuridae (sac-winged bats)

• Pacific sheath-tailed bat (Emballonura semicaudata) EN ^IUCN

Family Molossidae (free-tailed bats)

• Florida bonneted bat (Eumops floridanus) VU ^IUCN

Family Phyllostomidae (leaf-nosed bats)

• Mexican long-tongued bat (Choeronycteris mexicana) NT ^IUCN
• Greater long-nosed bat (Leptonycteris nivalis) EN ^IUCN
• Lesser long-nosed bat (Leptonycteris yerbabuenae) NT ^IUCN
• Red fruit bat (Stenoderma rufum) NT ^IUCN

Family Pteropodidae (megabats)

• Mariana fruit bat (Pteropus mariannus) EN ^IUCN
• Samoa flying fox (Pteropus samoensis) NT ^IUCN
• Guam flying fox (Pteropus tokudae) EX ^IUCN since 1960s

Family Vespertilionidae (vesper bats)

• Gray bat (Myotis grisescens) NT ^IUCN
• Indiana bat (Myotis sodalis) NT ^IUCN

Family Nesophontidae (West Indies shrews)

• Puerto Rican nesophontes (Nesophontes edithae) EX ^IUCN since 1500s

Family Soricidae (shrews)

• Pribilof Island shrew (Sorex pribilofensis) EN ^IUCN

Family Leporidae (rabbits and hares)

• Columbia Basin pygmy rabbit (Brachylagus idahoensis) LC ^IUCN
• White-sided jackrabbit (Lepus callotis) NT ^IUCN
• European rabbit (Oryctolagus cuniculus) NT ^IUCN (introduced from Western Europe)
• Appalachian cottontail (Sylvilagus obscurus) NT ^IUCN
• Robust cottontail (Sylvilagus robustus) VU ^IUCN
• New England cottontail (Sylvilagus transitionalis) VU ^IUCN

Family Cricetidae (true hamsters, voles, lemmings, and New World rats and mice)

• Red tree vole (Arborimus longicaudus) NT ^IUCN
• California red tree mouse (Arborimus pomo) NT ^IUCN
• Beach vole (Microtus breweri) VU ^IUCN
• Allegheny woodrat (Neotoma magister) NT ^IUCN
• Florida mouse (Podomys floridanus) VU ^IUCN
• Salt marsh harvest mouse (Reithrodontomys raviventris) EN ^IUCN

Family Geomyidae (gophers)

• Desert pocket gopher (Geomys arenarius) NT ^IUCN

Family Heteromyidae (heteromyids)

• Texas kangaroo rat (Dipodomys elator) VU ^IUCN
• Giant kangaroo rat (Dipodomys ingens) EN ^IUCN
• Fresno kangaroo rat (Dipodomys nitratoides) VU ^IUCN
• Banner-tailed kangaroo rat (Dipodomys spectabilis) NT ^IUCN
• Stephens's kangaroo rat (Dipodomys stephensi) EN ^IUCN
• White-eared pocket mouse (Perognathus alticolus) EN ^IUCN

Family Sciuridae (squirrels)

• San Joaquin antelope squirrel (Ammospermophilus nelsoni) EN ^IUCN
• Utah prairie dog (Cynomys parvidens) EN ^IUCN
• Palmer's chipmunk (Neotamias palmeri) EN ^IUCN
• Idaho ground squirrel (Urocitellus brunneus) VU ^IUCN
• Townsend's ground squirrel (Urocitellus townsendii) VU ^IUCN
• Washington ground squirrel (Urocitellus washingtoni) NT ^IUCN
• Mohave ground squirrel (Xerospermophilus mohavensis) NT ^IUCN

Family Dugongidae (dugong and Steller's sea cow)

• Steller's sea cow (Hydrodamalis gigas) EX ^IUCN since 1760s

Family Trichechidae (manatees)

• West Indian manatee (Trichechus manatus) VU ^IUCN
  • Florida manatee (T. m. latirostris) EN ^IUCN
  • Antillean manatee (T. m. manatus) EN ^IUCN

• List of mammals of the United States