It has been estimated that religious organizations own up to 25 percent of the land in the U.S. Which means 25 percent is exempt from taxation.
An 8-part New York Times series by Diana Henriques dissects the church exemption issue.
Getting rid of these unnecessary subsidies would be one of the quickest and easiest ways to clean up tax law, and get revenue into the public coffers. Allowances are understandable when services are being provided for the sick, poor, or elderly - those who can not afford it or are physically unable to provide for themselves. But the massive conglomerates and operations some religious organizations run and/or are involved with, which get tax exemptions, are market distortions favoring one group (churches) against others involved in provision of the same service.
For Further Reading:
Milwaukee County Tax Exempt Organizations
Sales Tax Exemptions For Non-Profit Organizations
Tax Burden Shifting: Exemptions
Why Do We Give Churches Tax Exemptions?