In sweeping Republicans off the Delaware County Council and gaining majorities on the boards of commissioners in Chester and Bucks Counties, Democrats made history Tuesday.

For the first time, they will have the lead role in shaping policy in all of Philadelphia’s collar counties — home to 20% of the state’s population.

In Delaware County, where Democrats will take all five County Council seats, that means cleaning house.

“The voters really spoke loudly and clearly yesterday by rejecting the current system,” Elaine Schaefer, who with Monica Taylor and Christine Reuther won the three open council seats, said Wednesday. “It was a conscious decision not just to elect Democrats but to elect people who didn’t want to keep doing things the way the very entrenched Republican machine has been doing things for generations.”

Almost immediately, the council members plan to conduct a “complete reassessment” of the way the county conducts its business and “whether we can do it better,” Schaefer said.

“This is the morning after, and we’re not in spiking-the-football mode,” she said. “We are in ‘Let’s start planning for a good government in Delaware County’ mode.”

Tuesday night, Delaware County GOP Chair Tom McGarrigle said the winners’ ambitious agendas ultimately would be costly for county residents: “I feel bad for Delaware County because they left the best team on the field and the taxpayers lost.”

From increasing affordable housing to expanding social services and protecting open space, newly elected Democrats say they are planning to continue policies that have worked while enacting more progressive policies in response to voters who clearly wanted change.

Delaware County Council members say they will implement a robust ethics policy, overhaul hiring to dismantle the patronage system, deprivatize the county prison, fund economic development throughout the county, invest in open space and trails, and reprioritize spending overall.

They want to create a countywide health department, joining the six of Pennsylvania’s 67 counties that have their own departments. The two Democrats already on the council made an issue of the county’s lack of a health department in the 2017 election. Republicans have long held that the county does not need a health department.

As the results of the election became clear late Tuesday, McGarrigle lamented the outcome. He said the GOP’s “message was simple: On council, we have three individuals who pledged never to raise taxes.... But I guess our message didn’t sink through to the taxpayer that we had great candidates who truly, truly cared about Delaware County.”

Wednesday morning, blue election signs still stood on street corners in Media calling out to drivers: “Had Enough TRUMP? FLIP DELCO.” Delaware County Democrats used similar messaging in 2017′s municipal election, when the first Democrats in history made it onto the council.

But Philadelphia’s collar counties have been trending blue since before Donald Trump became president, as more Philadelphia residents moved to the suburbs and the region’s demographics shifted. Republicans had a 5-1 voter registration advantage over Democrats in Delaware County 60 years ago. Now, 55% of registered voters are Democrats.

The Montgomery County Board of Commissioners has been under Democratic control since the 2011 election of now-Pennsylvania Attorney General Josh Shapiro and now-Transportation Secretary Leslie S. Richards.

“This is not just an anti-Trump movement,” said Robert Harvie, chair of the Falls Township Board of Supervisors and one of the incoming Democratic Bucks County commissioners. He said the political landscape of the county had changed.

Before Tuesday, the last time Democrats gained the board majority was in 1983. The Democratic hold lasted just four years before the party was ousted.

It used to be that the county’s Democratic Party had trouble finding candidates to run for positions because of Republicans’ many years of county control. “And now they are being challenged,” Harvie said.

In the earliest hours of Wednesday morning, 12 years after Bucks County Commissioner Diane Ellis-Marseglia was first elected, she stood before a raucous crowd in a backroom at Maggio’s Restaurant in Upper Southampton Township to chants of “Di-ane! Di-ane!”

“I’ve never been a majority commissioner before,” she said with a smile, drawing cheers from supporters at the county Democratic committee’s election night party.

Wednesday afternoon, Ellis-Marseglia was thinking ahead to what she wanted to accomplish now that she was on the majority side.

“I am so honored and thrilled to have this opportunity, and I am very grateful to the voters for entrusting us with this beloved county,” she said.

A social worker for the last 35 years, she is focused on adding staff to the Children and Youth Social Services Agency, expanding diversionary drug court, and creating a court specifically for people with mental illnesses, causes she has been talking about for years.

“I think locally, there is a concern about mental health and addiction and those social services counties deliver,” Ellis-Marseglia said. The opioid crisis has touched so many lives, she said, that it has made people realize that problems related to drug addiction and mental health are intertwined. She wants to improve communication among the social services departments.

“I felt like people were looking for, ‘Let’s do something to help people and deliver better services in the county so people get well,’” she said.

Downingtown Mayor Josh Maxwell and businesswoman Marian Moskowitz, Democrats who won seats on the Chester County Board of Commissioners for the first time in history, said they plan to expand public transportation and increase support for social services, especially those for crime victims. They also say they will continue preserving open space, focus on making county government environmentally sustainable, and look for ways to promote more affordable housing in the county, one of the wealthiest in Pennsylvania.

“There’s a lot of great stuff going on in this county; we have a great county,” Moskowitz said. “We can just build on that and make us an even better county.”

Staff writer Justine McDaniel contributed to this article.

Correction: A previous version of this story incorrectly said that 1983 was the only time Democrats had a majority on the Bucks County Board of Commissioners. It was the most recent time.