Under the federal Emergency Planning and Community Right-to-Know Act of 1986 (EPCRA), affected companies must report on- and off-site disposal or other releases to the environment of more than 650 toxic chemicals. The 18th Annual Toxic Chemical Report documents reported releases of toxic chemicals in Illinois for calendar year 2004, the most recent data available. In 2004, 1,215 facilities in Illinois reported toxic chemical releases of 135,002,481 pounds, which is the 9th largest amount among states. The most common type of release was air emissions, accounting for approximately 39 percent of reported releases. The top five Illinois counties for reported toxic releases were: 1. Peoria 2. Cook 3. Madison 4. Tazewell 5. Montgomery. Total releases in 2004 increased slightly from 131,778,756 pounds reported for 2003. There have been substantial reductions in Illinois and nationally since reporting began in 1988. Although it is difficult to compare annual data because of changes to the reporting requirements over the years, the downward trend in releases is apparent. For example, using a 1988 baseline, which only includes the chemicals and industries that were subject to reporting in 1988, releases in Illinois have declined from nearly 130 million pounds in 1988 to about 60 million pounds in 2004. Using a 1998 baseline, which includes chemicals and industries added to the reporting requirements from 1988 through 1998, releases declined from approximately 165 million pounds in 1998 to 135 million pounds annually in 2004. In assessing this data, it is important to understand what counts as a release under EPCRA. For example, toxic chemicals that are treated in certain ways, recycled or used to make energy are not counted as released to the environment. Understanding the limitations of this data is also important. For example, although EPCRA captures most of the toxic chemicals currently being used by covered industry sectors, it does not cover all chemicals or all sectors. Facilities that do not meet the reporting threshold levels are not required to report, and the toxic release data does not include emissions from mobile sources nor releases of pesticides, volatile organic compounds, and fertilizers from many other non-industrial sources. In addition, release estimates alone are not sufficient to determine human exposure or to calculate potential adverse effects on human health and the environment. Additional information is necessary to assess exposure and risk, although toxic release data can be used to identify areas of potential concern. The data in this report was compiled by the U.S. EPA based on Toxic Release Inventory reports received as of November 18, 2005.