Belle Fourche was home to 5,594 people at the time of the 2010 Census. With a median age of 36, the population of Belle Fourche is growing rapidly. Since the 2000 Census, it has posted a growth of 22.5 percent.  In the city of Belle Fourche, there are 658.1 people per square mile.

The majority (93.6 percent) of people in Belle Fourche are white.  American Indians constitute 2.1 percent of  Belle Fourche’s population and 4.1 percent are Hispanic. In 2010, 2.6 percent of the population reported belonging to more than one race.