|Sport||Baseball Class D|
|Ceased||1948 (became Mississippi-Ohio Valley League in 1949)|
|No. of teams||6|
|Most titles||1 Belleville Stags (1947)|
West Frankfort Cardinals
|Official website||Midwest League Official Website|
The Illinois State League (ISL) was a baseball minor league formed in 1947. The league operated in 1947-1948 and evolved to become today's Midwest League. The Class D ISL was composed entirely of new franchises, each located in Southern Illinois. The charter franchises were in the Illinois cities of Belleville, Centralia, Marion, Mattoon, Mount Vernon and West Frankfort. The ISL was renamed the Mississippi-Ohio Valley League after the 1948 season as the Marion Indians moved to the State of Kentucky to become the Paducah Chiefs. Subsequently, the Mississippi-Ohio Valley League operated through 1955 and in 1956 changed names to become the Midwest League.
The league President was Howard V. MIllard. The ISL had the same six teams in both of its seasons: the Belleville Stags, Centralia Cubs, Marion Indians, Mattoon Indians, Mount Vernon Kings, and West Frankfort Cardinals. In 1947, the league began play and established a 120-game season and played two halves. There was no championship series in 1947 because Belleville won both halves. In 1948, the West Frankfort Cardinals finished 85-35 and then swept the Mattoon Indians in three games in the Championship Series.
The Illinois State League held an annual All-Star Game. The first All Star Game was held on August 12, 1947 at Memorial Stadium in West Frankfort, as the ISL All-Stars defeated Belleville 5-1. The 1948 Illinois State League All-Star Game was July 12, 1948 at Mattoon Baseball Park. The All-Stars defeated Mattoon 1-0.