The mobile phone alert, which was also mistakenly sent to people in OR, urged people to call a number with a 360 area code.
The 911 outage affected agencies across Washington state on Thursday night and continued into Friday.
The head of the Federal Communications Commission said he has directed the FCC's public safety staff to launch an investigation into the nationwide outage.
The Clark County Emergency Services Agency sent the first of two alerts Thursday evening at around 11:22 p.m., warning that "911 lines are down in our area". The outage affected only wireless 911 calls, not landline calls, CNN affiliate WBZ reported.
In Idaho, the internet problems caused the temporary shutdown of phone services at the Idaho Department of Correction and the state's Department of Education, The Idaho Statesman reported.
The effect on people's ability to reach 911 emergency services is "completely unacceptable", he said.
"We will continue to monitor this situation closely to ensure that consumers' access to 911 is restored as quickly as possible", Pai said.
What's going on: Customers across the nation said they experienced internet power outages from CenturyLink, according to Newsweek.
"Our network is experiencing a disruption affecting customer services".
According to NewsWeek, Centurylink services have been down most of the day, and customers have been having trouble getting in contact with CenturyLink's support department.