The reindeer population numbers in the low millions as of 2015, but exact figures are not available because their herds and population groups are in constant flux and are located over large tracts of land that cannot be monitored constantly or accurately. In 2015, many of the world's largest reindeer and caribou populations were in a state of decline and were suffering from human over-hunting and other factors.
The largest reindeer herd in Alaska, the Western Alaskan herd, reached its peak size of 490,000 in 2009, but by 2011 it had declined to 325,000. This steep reduction in numbers prompted consideration of reducing the yearly culls that help to thin herds.
Russia's largest herd numbers roughly 700,000 animals, a number that fluctuates rapidly based on the presence or absence of subsidies for hunters. The government incentivizes hunting when population explosions seem imminent and the deer are in danger of destroying their own food sources and bringing on famine.
Global reindeer population levels are not regular or balanced and have been known to swing wildly over just a few short years. Many countries are involved in ongoing efforts to stabilize their native populations and to protect deer both from exploitation and from overpopulation.