Chinook was plunged into darkness for about six hours Monday night when equipment that controls voltage at NorthWestern Energy's substation failed.
NorthWestern spokesman Butch Larcombe said 1,131 customers — most of the city — were without power.
One regulator failed and prompted a second regulator to go out.
The power stopped at 5:31 p. m., he said. By 11:30, power was restored to the entire community.
Larcombe said the outage may have been weather-related, from problems caused by recent snow and cold weather, or it may have been caused by animals in the area.
"Our first priority was to get the power back on," he said. "Today, we will be looking around trying to find the cause."
One thing that helped crews restore power, he said, was that a temporary substation had been brought in next to the regular substation.
The temporary equipment was going to be used starting Nov. 26, when major repairs are planned to the substation.
Some equipment from the temporary substation was quickly moved to the permanent substation, he said, speeding up the repair process.
The repairs are part of a major upgrade that NorthWestern is planning for its entire system.
The substation near Harlem recently underwent a similar upgrade, he said.