It’s becoming common knowledge that the U.S. imprisons more of its population than any other nation. In 2011, the Bureau of Justice Statistics reported that there were 1.6 million state and federal prisoners.

While state prisons have seen a small decrease in their populations over the past couple of years, prisoners in the federal system continue to increase. Last week, the Congressional Research Service (PDF) published a new report that provided data about the federal prison population. It found that there were about 219,000 inmates under federal Bureau of Prison’s (BOP) jurisdiction in 2012 — a nearly 790 percent increase in 32 years.

The key part of the report is summarized in an article by Ashley Portero:

Since 1998, individuals arrested for drug crimes have constituted the largest portion of federal prison admissions, followed closely by those arrested for immigration and weapons-related offenses. Meanwhile, the CRS reports there has been a significant drop off in the number of inmates entering prison for violent or property-related crimes, which only made up about 4 percent and 11 percent of prison admissions in 2010.

A huge portion of those drug offenders are arrested for marijuana offenses, even though the substance – now legal in 18 states for medicinal use– has become increasingly mainstream. However, statistics from the Federal Bureau of Investigation reveal more people were arrested for marijuana possession than all violent crimes combined in 2011.

If it continues to grow at the same rate, the Urban Institute predicts the federal prison system will eat up as much as 30 percent of the Department of Justice’s budget by 2020. The group reports the rapid population increase has mainly come from imposing longer sentences, and not a higher arrest rate. Drug offenders are often the targets of those sentences.