In what year was the team founded that won the 1956-1957 Irish League championship?
1956–57 Irish League The Irish League in season 1956–57 comprised 12 teams, and Glenavon won the championship.
League of Ireland First Division The League of Ireland First Division (Irish: "Céad Roinn Sraith na hÉireann" ), also known as the SSE Airtricity League First Division, is the second level division in both the League of Ireland and the Republic of Ireland football league system. The division was formed in 1985. It replaced the League of Ireland B Division as the League of Ireland's second level division. Since 2003 the First Division has operated as a summer league.