The Wabash River is a 503-mile-long river that drains most of the state of Indiana, and a significant part of Illinois, in the United States. It flows from the headwaters in Ohio, near the Indiana border, then southwest across northern Indiana turning south near the Illinois border, where the southern portion forms the Indiana-Illinois border before flowing into the Ohio …The Wabash River is a 503-mile-long river that drains most of the state of Indiana, and a significant part of Illinois, in the United States. It flows from the headwaters in Ohio, near the Indiana border, then southwest across northern Indiana turning south near the Illinois border, where the southern portion forms the Indiana-Illinois border before flowing into the Ohio River.