Macomb, IL – The value of Illinois farmland has dropped about 10 percent yearly for the past three years. Now it's about to fall even more. The Illinois Department of Revenue is issuing a lower productivity index on some farmland. The index rates the potential of the more than 700 soil types in the state. McDonough County Supervisor of Assessments Tammy Clamp says the change might cut the income of taxing bodies with a lot of rural property. Her office is preparing letters to notify landowners of the coming change.