Despite Hamilton County’s reputation as a magnet for new residents, two smaller central Indiana counties and one near Louisville outpaced its population growth rate in 2025. Meanwhile, Marion County, the state’s largest, lags behind.
Indiana added more than 38,000 residents from July 2024 to July 2025 to reach a total population of 6.97 million, according to new census data analyzed by the Indiana Business Research Center at Indiana University.
Seven of the state’s 10 fastest-growing counties were in the 11-county Indianapolis metropolitan area. Statewide, 66 of Indiana’s 92 counties reported an increase in residents, and the overall growth rate slightly outpaced the nation’s.
But Indiana’s growth is projected to slow significantly in the coming decades as natural increase — births outnumbering deaths — gradually reverts into natural decrease.
Indiana has already started to rely heavily on migration, with 80% of population growth in the last three years due to people moving from abroad or within the United States. This shift upends the post-World War II norm of natural increase driving the state’s growth, said Matt Kinghorn, senior demographer at the IBRC.
“As the baby-boom generation ages, at the same time as fertility rates decline and as the health of our population struggles, we’re seeing natural increase decline significantly,” Kinghorn told IndyStar. “Ten to 15 years from now, we expect for Indiana as a whole to start seeing natural decrease, where deaths outnumber births.”
Top 10 fastest-growing Indiana counties in 2025
Hamilton County gained more than twice as many residents as any other Indiana county in 2025, bringing its current population to about 387,000.
But for the third consecutive year, the smaller doughnut counties of Boone and Hancock grew faster. Boone County is home to the surging small cities of Zionsville and Lebanon, while Hancock County includes Greenfield and part of Cumberland.
“Smaller, emerging counties typically can have a faster rate of growth just because they are new frontiers,” Kinghorn said, “whereas Hamilton County has been the stalwart for growth in the state for decades.”
Here are the Top 10 counties by growth rate from July 2024 through June 2025, including their new total number of residents:
Where Marion County’s population growth ranked
Marion County, which now has about 992,000 people, grew at a much slower rate than most central Indiana counties. Adding about 2,000 residents, Marion County’s 0.2% growth rate ranked No. 50 statewide.
In major metros around the country, especially in the Midwest, suburbs have grown more quickly than the core cities they surround for the past half-century, Kinghorn said.
Notably, the only counties outside the Indy metro to crack the Top 10 were Clark County, near Louisville; Parke County, the west-central Indiana community that hosts the annual Covered Bridge Festival; and Owen County, in the Bloomington area.
“What you’ve seen with a lot of communities around central Indiana is a longstanding investment in quality of place and economic development,” Matt Greller, CEO of Accelerate Indiana Municipalities, told IndyStar. “Those two things coupled together have resulted in the population growth that we’re seeing.”
Migration fuels growth while birth rate falls
Immigration from outside the United States was Indiana’s leading source of growth from 2024 to 2025, followed by domestic migration within U.S. borders. Together, they brought more than 30,000 new residents.
New births, meanwhile, accounted for only about 8,500 new residents. Indiana’s rate of natural increase declined for the first time in four years after a pandemic rebound, Kinghorn said.
Migration has propped up Indiana’s rural and mid-sized counties in particular, Kinghorn said. Most of these communities can grow only by attracting new residents.
But relying on migration as a buffer against an aging population is likely unsustainable. Already, the Trump administration’s immigration crackdown appears to be reducing the number of new residents, Kinghorn said. Net international migration to Indiana declined by more than 50% from 2024 to 2025, the data shows.
“I would expect that we’ll continue to see the role that immigration plays in our population growth diminish even more over the next few years, at least,” Kinghorn said.
As the baby boomers age and birth rates lag, the IBRC projects that Indiana’s growth rate will fall dramatically over the next four decades. The state is expected to add roughly 383,000 residents through 2060 — fewer than Indiana gained in one decade from 2000 to 2010 — bringing its total population to nearly 7.2 million.
Email Indianapolis City Hall Reporter Jordan Smith at JTSmith@indystar.com. Follow him on X @jordantsmith09 and Bluesky @jordanaccidentally.bsky.social.
This article originally appeared on Indianapolis Star: These 10 Indiana counties grew fastest in 2025, as migration fuels growth
Reporting by Jordan Smith, Indianapolis Star / Indianapolis Star
USA TODAY Network via Reuters Connect
