This article deals with the issue of King John Casimir’s copper shillings struck in 1659–1666, emerging from the analysis of the structure of large shilling hoards in relation to the contents of mint reports. It was conducted on the basis of representative, newly-described finds from Idźki-Wykno and Rokitno, as well as previously published deposits, encompassing more than 59,000 coins. On this basis, the global production volume of shillings was estimated along with the share of individual mints. These values prompt a response to the accusations of mintage abuse levelled against Tytus Livius Boratini. However, another premise emerged from the initial analysis of false shillings that helps to date hoards of copper shillings.