MANKATO — Eleven genetically rare bison have been released into a state park near Mankato as part of an effort to expand the bison herd in Minnesota.

The Department of Natural Resources says there were once an estimated 30 million to 60 million bison in North America. During the 19th century, bison were hunted to near extinction, and less than 1,000 remained in the U.S.

The last wild bison in Minnesota was seen in Norman County in 1880.

Bison were reintroduced to the state in 1961.

In 2012, the Minnesota Zoo and DNR agreed to work together to preserve the American bison and grow the herd to 500 animals in several locations. The new bison were released Friday into Minneopa State Park near Mankato.