Modifies provisions governing city-county library boards of trustees in St. Charles County

HB 1405 enables cities and St. Charles County to merge their separate library systems under specific conditions, such as matching library tax levies and a county population under 250,000. The bill establishes rules for appointing a nine-member board of trustees for the merged library, based on population comparisons between the city and county, with a detailed process for the four most populous cities in counties with 400,000-500,000 residents starting in 2026. It requires transferring all unexpended funds, property, and tax responsibilities from the separate systems to the merged library, which will operate as a county library district under state law.