Authorities are seeking a walkaway from the Passages women's pre-release center.
Sienna Sunn-Plainbull, 31, is 5 feet 3 inches tall and 155 pounds with black hair and brown eyes. She walked away around noon Friday.
Sunn-Plainbull was sentenced for attempted robbery out of Yellowstone County and arrived at the Passages program on Nov. 11.
Call 911 if you have any information on her whereabouts.