"Right now what they're doing is conducting a forensic audit of the situation so that they can kind of see what happened," said Contra Costa County Supervisor Diane Burgis.
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In Pleasant Hill, the police department says the incident directly hit the city's computer infrastructure.
And in Oakley, officials there declared a local emergency immediately following the attack.
As of Monday, they tell ABC7 News while some departments have returned to near-normal levels, others are still being impacted by the attack.
"Things are coming back online. Their belief is things are controlled. But things are always gradually brought back up to make sure that security won't be compromised," said Contra Costa County Supervisor John Gioia.
RELATED: Hayward city service coming back online following ransomware attack
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Cyberattacks like these against local governments are becoming increasingly common.
Just last year, Oakland was devastated by a major ransomware attack that crippled the city for weeks.
"It's really a financial motive for these bad actors. They want to intrude into the network, they want to lock down data and systems and then demand a ransom payment," said Sai Huda.
Huda is a cybersecurity expert and the CEO of Cybercatch.
He says given the growing trend of cyberattacks on smaller governments, it's important for them to be prepared.
RELATED: Dozens of Oakland ransomware victims never notified SSN were leaked on dark web, I-Team finds
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"Generally they will look for the consumer data that involves high value. So they're looking for social security numbers, driver's license information," said Huda.
Contra Costa officials say while they've improved cyber security measures across the county in recent years, they're always looking to do more.
A job that falls both on elected officials, and individuals.
"It's so important whether at work, or home, or on our phones, that we are being very careful about the things that we open, the sites that we go to," said Burgis.