As of June of 2014, there are around 500,000 bison in the United States. This is an ever-growing number that is expected to nearly double.
During the beginning days of America and as early as the late 1700s, there were approximately 30 million bison that roamed around the country. This number is a rough estimate and could very well be much higher. Journals that were a part of the Lewis and Clark expedition described the herds as darkening the plains. Travelers said it could take up to six days to cross through a heard of bison.
Although the number of bison was high during early days, it began to quickly decline during the 19th century to the point that there were less than 1,000 bison left in America at the beginning of the 20th century. The bison population quickly declined because there were many things going on around their lands at the time. Indians acquired guns and could more easily slaughter the bison for protection and to have a steady amount of meat, there was a heavy drought that caused their land to dry up and settlers began to take over the land that was once inhabited by bison.
Under the direction of Theodore Roosevelt, the bison began to be protected. Programs were created to help raise the population and these programs are expected to continue indefinitely.