Standard & Poor's pushed the rating to "AAA" from "AA+," where it had stood since 2006.
The was due in part to property tax reform, low-overall state debt levels, a stable and diversifying economy, and relatively conservative biennial budget.
The new rate reflects the state's "continued strong management that has led to the property tax reform that has realigned state and local spending and is not expected to impact the state's long-term financial performance," S&P said.
"As well, the state's commitment to attract diverse jobs through its economic development efforts has translated into a shift away from traditional manufacturing employment."
Gov. Mitch Daniels, who hopes to win a second term as governor, said in a statement that the rating shouldn't be taken for granted. "Our own history and the current tumbles of other states show that continued careful management is key, because it's too easy for these gains to slip away."
Indiana's credit rating was lowered twice between 2002 and 2004.
Other states with an AAA credit rating are Delaware, Georgia, Maryland, Minnesota, Missouri, North Carolina, Utah and Virginia.