MainSource said the transaction brings a long-desired presence in Kentucky. 1st Independence has eight branches in Kentucky and Indiana.
The deal has been approved by directors of both banks and is expected to close in the third quarter.
Today's announcement comes less than a month after MainSource said its CEO, James L. Saner Sr., had resigned. MainSource did not explain the departure of Saner, who had been with the bank for 11 years.
Greensburg is between Indianapolis and Cincinnati, and is the location of the new Honda Manufacturing of Indiana auto-assembly plant.