WASHINGTON -- A private foundation will give out millions of dollars in grants to local jurisdictions that agree to try new ways to safely reduce the number of people in jails.

The John D. and Catherine T. MacArthur Foundation on Wednesday announced the Safety and Justice Challenge that will award $75 million over five years to counties and cities that find strategies to trim the number of people in jails and the length of their incarceration.

The project aims to reverse the sharp increase in the U.S. jail population, which has more than tripled since the 1980s to 12 million jail admissions per year. Jails, which usually hold prisoners awaiting trial or serving short sentences, are "where over-incarceration begins," the foundation said.

"We've seen dramatic decreases in the number of people who go to jail in particular jurisdictions," Laurie Garduque, director of justice reform for the MacArthur Foundation, said in an interview with The Huffington Post ahead of Wednesday's announcement. "So we know that it can be done, it just has to be done on a broader scale and nationally."

Garduque said that the project will be a collaboration with other organizations and will draw from work already done.

"We know that local problems require local solutions," Garduque said. "The aim is to show that, regardless of your starting point, you can make changes in terms of improving your justice policies and practices."

Jails in the U.S. are being stuffed with an increasing percentage of the population, according to a study released Wednesday by the Vera Institute for Justice. In 2013, 231 people per 100,000 were in jail at any one time, compared with 96 people per 100,000 in 1983. While jails were historically intended to detain people awaiting trial who were a flight risk or a danger to the public, the Vera Institute report says prisoners today often fit neither category.

The MacArthur Foundation challenge will select up to 20 jurisdictions to receive a grant of $150,000 each and a consultant from May through December. As many as 10 of those localities will be eligible for up to $2 million per year to implement the plans they developed.