The writing was on the wall. In the 2018 midterm elections, a Democrat was elected to represent Chester County in Congress for the first time since the 1850s. Then, last year, Democrats took control of the county’s Board of Commissioners for the first time ever.

And now, the party is celebrating another milestone: Data released this week show registered Democrats outnumber Republicans in Chester County, apparently for the first time — by 228 voters.

As of Monday, there were 148,194 registered Democrats in the county compared with 147,966 Republicans, according to data compiled by the Pennsylvania Department of State. An additional 61,895 voters were either registered with another party or unaffiliated.

“Anyone who has lived in Chester County since George W. Bush won the White House knows the enormity of this moment,” Dick Bingham, chairman of the Chester County Democratic Committee, said in a statement Tuesday.

The development comes as Republicans have continued to struggle in suburban areas outside Philadelphia and across the country. Democrats already outnumbered Republicans in Bucks, Montgomery, and Delaware Counties.

Since 2000, Philadelphia’s four collar counties have steadily become more racially diverse, better educated, and home to more young adults. These demographic changes have coincided with, and helped fuel, increasing Democratic registrations.

The trend has accelerated since the election of President Donald Trump in 2016, as the Republican Party has increasingly become home to white working-class voters and people living in rural areas. While Democrats have swept to power outside Philadelphia, they have suffered losses in former strongholds in western Pennsylvania.

Chester County GOP Chairman Rick Loughery said the data showed the importance of independent voters in the county. “Once we get through the [June 2] primary, I’m confident our Republican candidates will make a compelling appeal to all voters,” he said.

So far this year, 2,099 Chester County residents have switched their registration from Republican to Democratic — and a similar number of voters previously unaffiliated with either party have also registered as Democrats. Just 394 voters have switched their registration from Democratic to Republican this year.

Ten years ago, Republicans outnumbered Democrats by nearly 25,000 registered voters in the county. By May 2018, the GOP still had an edge of more than 15,200.

Bingham said the party “noticed the seismic movement among our neighbors” that year when Democrat Chrissy Houlahan was elected to Congress and the party also won several state House races. Houlahan also benefited from a decision by the Democratic-led state Supreme Court that redrew Pennsylvania’s map of congressional districts.