"Black-eyed susan" is a common name for a few different flowers which look very similar, but actually belong to several different species of the Rudbeckia genus. Not every Rudbeckia is a black-eyed susan. This article focuses on the species that are called black- or brown-eyed susans: R. fulgida, R. hirta, and R. triloba, and also covers the similar-looking sweet coneflower, R. subtomentosa.
Although these species look similar and have similar habitat preferences, there are significant differences in their growth habit and ideal growing conditions. By knowing these distinctions, you will be able to better utilize these plants in your garden, as well as identifying them in the wild, which can be useful if you want to grow a particular species from seed.
All of these plants are native to Eastern North America, and R. hirta has a wide native range, across most of the continental U.S. and into Canada. Wherever you are, I recommend only planting locally native plants, so as to maximize your positive impact on the environment. Check that you are in the range of these species before planting them in your garden.