Butler County is experiencing the slowest growth in its history.

Data released Thursday by the U.S. Census Bureau indicated the county's population in 2018 had grown to 186,566 residents — a 1.5 percent increase from the number in the decennial 2010 census. That growth is the lowest the county has seen since its inception in 1800.

These data stem from the American Community Survey, which the Census Bureau sends every year to around 3.5 million households. It released Thursday its five-year estimates, which the bureau lauds as its most accurate representation of population. These estimates are weighted averages of five years of survey results.

With the beginning of census polling four months away, this data likely indicates the direction in which the official decennial count will go.

The figure for Butler County is paralleled only by the slow growth in the county between 1860 and 1870, when its population rose 2.6 percent from 35,594 to 36,510.

But, county commissioners say, the numbers are still positive.

“We're one of the few, if not the only, counties in southwestern (Pennsylvania) that is” growing, said Leslie Osche, Butler County commissioner chairwoman.

Osche said a primary reason for the slowdown in growth may be that communities in southwestern Butler County are experiencing the same issue — they may have less room to develop than 10 years ago.

“I think we had a big influx, obviously, with the growth in Cranberry and then the growth in Adams,” Osche said. “I would say that, once you've saturated an area, you're obviously going to see a slower population growth.”

The population of Cranberry Township continued to grow, adding nearly 9 percent to its 2010 population of 28,098. The township now has 30,552 residents.

However, like the county, the township experienced slower-than-typical growth. Between 1940 and 1950, the last decade recording slower growth, Cranberry saw a 0.99 percent boost in its population, one-tenth of a percentage point less than its yearly 2010 to 2018 growth.

Another potential reason for the slowdown in growth, Osche said, is the demographic shifts.

“I think, funny as it seems, our young people don't seem to have as many children as they used to have,” she said.

The five-year estimates indicate that the county's median age went up by two years, to 43.5 years old. The share of the population under 18 decreased to 20.5 percent from 22.4 percent, while the portion aged 65 or older increased 1.6 percentage points, to 17.7 percent.

Not all slowdowns were negative, however.

The City of Butler has not seen a population increase in census data since 1940. The population has decreased in the city from 24,477 in 1940 to 13,757 in 2010.

But the five-year estimates indicate the shrinkage is slowing down, as the number of Butler residents lowered just 4 percent from 2010 to 2018. That's a far cry from the 9 percent decrease that occurred from 2000 to 2010 and the 7 percent or more decreases nearly every decade since 1950.

“The stability of our workforce and our economy and business, the stability of all that in this county and the fact that it's extremely resilient shows why people want to move here,” Osche said.

“I think there's just a lot to offer in Butler County, and people see that.”