Hamilton County, Indiana is north of Marion County and Indianapolis. It has grown seven-fold since 1970, from 54,000 to more than 365,000 people. It now ranks in the top 7% as the 209th largest county of the 3,142 in the US. It is the fourth largest of Indiana’s 92 counties, trailing Marion (Indianapolis), Chicago’s suburban Lake County and Allen County (Ft. Wayne) which it will surpass for third place in 2029.

The county has averaged a 7,800 person annual increase since 1990 and has maintained a 7,500-person annual increase in the last decade.

Growth reached a peak of 12,000 per year prior to the Great Recession, dropped back to 7,000 per year and has slowly grown to 8,000 per year.

As a growing suburban area, the county has benefitted from a younger population with relatively more births and less deaths. This demographic advantage has decreased through time.

On average, this natural increase advantage has provided 2,000 additional people each year for the last two decades. The net in-migration level was over 8,000 before the Great Recession, dropped in half to 4,000 before recovering to about 6,000 people per year.

The US Census Bureau’s American Community Survey (ACS) attempts to measure the annual migration flows between all 3,142 counties! It’s survey techniques generally require a 3-5 year sampling period to have statistical reliability. The US Census Data and the Indiana Vital Statistics Data (Births and Deaths) show an implicit net in-migration to Hamilton County from 2011-20 of 4,575 annually. The ACS reports just 3,124. The actual increase is 144% of the surveyed increase.

https://www.census.gov/topics/population/migration/guidance/county-to-county-migration-flows.html

https://www.stats.indiana.edu/vitals/

https://wonder.cdc.gov/controller/datarequest/D158

Cross-County Migration

Hamilton County’s population ranged from 283-346,000 between 2011-20, for an average of 314,000. Inbound migration averaged 23,600 per year or 7.6% of the population. Outbound migration averaged 20,400 per year or 6.6% of the population. On average, the county’s population turns over every 15 years. The net in-migration in the ACS survey was 3,100, a little more than two-thirds of the implicit 4,600 net in-migration per year. I compared the 2011-2015 and 2016-2020 data and found that they were generally consistent. I believe that the proportions reported are generally accurate.

International In-Migration

ACS reports an annual average of 1,800 international immigrants. This is 59% of the net 3,100 figure; quite material. On an annual basis, this is just 0.6% of the county population, but for a decade it is 6%. 61% of Hamilton County’s international immigrants report Asia as their home continent.

Total US Migration

Net in-migration to Hamilton County from the US is a positive 1,300 per year in the ACS survey, perhaps 1,900 including the 1.46X factor. Net domestic net in-migration is two-thirds the size of international net in-migration; 0.4% annually or 4% per decade.

48 States Aside from Indiana and Illinois

Net in-migration to Hamilton County from the other 91 counties in Indiana plus Illinois averages 3,004 per year, essentially equal to all of the total net in-migration. Net in-migration to Hamilton County from the other 48 states is a negative 1,700 per year, roughly one-half of the positive overall net in-migration figure. Hamilton County receives minor positive inflows from the adjacent states of Ohio, Michigan and Kentucky. It sends 1,000 residents to Texas each year and receives just 400 in return. Texas accounts for one-third of Hamilton County’s net out-migration aside from Indiana and Illinois. Hamilton County exports 1,200 residents annually to Florida but an equal 1,200 return each year.

Chicago, Illinois

In the last decade 1,500 people annually moved to Hamilton County from Illinois (Chicago) and just 700 returned the favor. Hamilton County received a net 800 residents from Illinois each year in the past decade. This is one-fourth of the net in-migration to Hamilton County. Many Hamilton County college graduates make Illinois their first professional home, so the flow of experienced professionals from Chicago to Hamilton County is probably more than 1,500 per year.

Marion County, Indiana (Indianapolis)

Hamilton County’s Carmel, Fishers, Westfield and Noblesville claim that they are “edge cities” somewhat independent of Indianapolis. In the last decade a net 3,300 migrants from Marion County chose to make Hamilton County their home each year, accounting for more than ALL of the ACS survey’s 3,100 annual increase. Marion County has nearly 1 million people and continues to grow slowly despite this 0.3% annual leakage to Hamilton County.

College Students

Hamilton County school graduates have very high college attendance rates. Hamilton County exports 2,600 students each year to IU, Purdue and Ball State and receives 1,000 back, for a net out-migration of 1,600 per year, about one-half of the net in-migration figure.

Indiana

Hamilton County has a minor net in-migration from sparsely populated Boone County to its west (300/year). It’s net in-migration with the 8 nearby counties, including Boone, is a 500 loss. Hamilton County is an attractive suburban destination, but net net it loses 500 residents annually to nearby counties other than Marion.

Setting aside Marion County and the 3 university counties, Hamilton County attracts 500 new residents annually from the other 87 Indiana counties.

Summary

Hamilton County enjoys a 2,000-person annual natural population increase due to its relatively young age profile. Half of its 6,000-person annual net in-migration is driven by international immigrants attracted to its schools, amenities, services and culture. Most of its remaining growth is driven by nearby Marion County residents who are seeking the same results. Hamilton County is attracting residents from Chicago as retirees, commuting residents or transplants. Hamilton County loses about 2,000 college students each year who migrate into a national labor market. This is an opportunity for further population growth. It also shows that the net 3,100 growth per year figure understates the attractiveness of this county to all potential migrants.