This paper investigates the economic impacts of the Composition for Tithes Act of 1823, focusing on the incremental revenue risks it imposed on tillage farmers in southeast and northeast Ireland. This reform of the tithe would see its longstanding design as an ad valorem production tax of 10 per cent converted into a lump-sum land tax. Crop farmers would therefore be permanently exposed to all revenue risks, not just 90% of such risks, and those of them who were very risk-averse were net losers under this reform. For many tillage farmers on large lots who could diversify and/or expand their activities to overcome this additional risk and for others who were not so risk-averse, their tithing rates would be discounted by as much as 88%, thereby offering a substantial temporary off-setting economic benefit until their rents were raised by an equivalent amount to the tithe discounts at the next renewal date of their lease. Indeed, this immediate savings induced a sufficient number of them within many parishes to agree to the reform of their tithe. Only in parishes heavily populated by extremely risk-averse cottiers would the composition of the tithe prove unacceptable. Therefore, when Parliament made the composition of the tithe compulsory in 1832, organized civil disobedience emerged – no doubt fuelled in part by longstanding religious tensions – armed police and militia countered and the affray conflagrated into what became known as the Irish Tithe War of 1831-1838 largely in the Catholic south, Munster and Leinster, where risk-averse cottiers were most prevalent. The social impacts of converting the tithe into a composition did not end with the cessation of this civil rebellion, however. Its additional revenuerisks persisted well into the next decade, increasing the financial vulnerability of small farmers and cottiers, particularly potato farmers who would come to experience an unforeseeable succession of broken harvests and who, more than others, would fall victim to the “Great Famine” of 1845-1850.