The Navajo County Sheriff's Office and the Navajo Nation have signed a cross-commission agreement that allows the agencies to police one another's territory.
Navajo President Ben Shelly says tribal members who report emergencies on the reservation can face long response times that can be shortened with a call to the sheriff's office.
The two-year agreement outlines the rules for enforcing the laws on the reservation and within Navajo County.
Similar agreements have been reached with other counties that include reservation land. The tribe is working on one with San Juan County in Utah.