This report presents a summary of air quality data collected throughout the State of Illinois during the calendar year - 2001. Data is presented for the six criteria pollutants (those for which air quality standards have been developed - particulate matter (PM10 and PM2.5), ozone, sulfur dioxide, nitrogen dioxide, carbon monoxide, and lead) along with some heavy metals, nitrates, sulfates, and volatile organic compounds. Monitoring was conducted at over 90 different site locations collecting data from more than 200 instruments. In terms of the Air Quality Index (AQI) air quality during 2001 was either good or moderate more than 89% of the time throughout Illinois. There were 40 days when air quality in some part of Illinois was considered Unhealthy for Sensitive Groups (17 for 8-hour ozone ,25 for PM2.5, and 1 day for PM10, 3 days were high for both ozone and PM2.5). This compares with 25 Unhealthy for Sensitive Groups days in 2000. The increase is more due to 2000 being a cleaner year in terms of weather patterns than an indication of worsening air quality. Air quality trends for the criteria pollutants are continuing to show downward trends or stable trends well below the level of the standards. Percentage changes over the ten year period 1992 2001 are as follows: Particulate Matter (PM10) 16% decrease, Sulfur Dioxide 34% decrease, Nitrogen Dioxide 4% increase, Carbon Monoxide 43% decrease, Lead 44% decrease, and Ozone 7% decrease. Stationary point source emission data has again been included. The data in the report reflects information contained in the Emission Inventory System (EIS) as of December 31, 2001. Emission estimates are for the calendar year 2000 and are for the pollutants: particulate matter, volatile organic material, sulfur dioxide, nitrogen oxides and carbon monoxide. Emission trends of these pollutants has been given for the years 1981 to the present. Emissions reported with the Annual Emissions Report have been provided starting with 1992. In general there has been a trend toward decreasing emissions over this time period.