I wish there was a simpler answer to your question!

Different countries have different definitions of "endangered" or"threatened" species and have different laws about the protection of the species. In the United States, laws are based mostly on the Endangered Species Act (ESA) of 1973. According to the ESA, the term"endangered species" means any species which is in danger of extinction throughout all or a significant portion of its range(except bug "pests"!) and "threatened species" means any species which is likely to become an endangered species within the foreseeable future throughout all or a significant portion of its range.So, it is up to law-makers and scientists to determine which species should be treated as "endangered" or "threatened". Globally, the World Conservation Union (IUCN) keeps a "Red List" of species, ranked by their conservation status: Critically Endangered (CR), Endangered (EN), and Vulnerable (VU). To determine how to classify a species,many factors are taken into account, not just the number of animals remaining, but also the overall increase or decrease in the population over time, breeding success rates, known threats, and other factors.For an idea though, some endangered species have had a 20% decrease in their populations over a few species generations, and some have lost80% or more, or only have less than 100 individuals remaining! So, the status depends on the specifics on the population and the success of the people who are researching and supporting protection of the species, among other points.

The government says that an Endangered species is "an animal or plant species in danger of extinction throughout all or a significant portion of its range."A threatened species is "An animal or plant species likely to become endangered within the foreseeable future throughout all or a significant portion of its range."

It's not as simple as a certain number. It depends on the species.Some species can reproduce quickly, so if their population gets low,they can bounce back fairly fast. Others reproduce very slowly, so if their numbers get low, they are in more danger. So two species may have the same population size, but one is in a lot more danger of extinction.

It also depends on what's happening to the habitat. Disease, introduced species, hunting, poisons, and other things can put a species in danger, but habitat destruction is the most likely to make a species go extinct. If the place a species lives is being destroyed, it doesn't help it to reproduce quickly or have a large population size.

Several species have come back after getting legal protection. I live in Wisconsin, where wolves are making a big comeback. Are there any species in your area that have recovered from being threatened or endangered?