Data from the Illinois State Police, the Administrative Office of the Illinois Courts, and other agencies indicate the numbers of reports and cases handled. These data sources provide much information, although they contain several gaps. The family violence data is particularly sufficient for describing victim and offender demographics and victim-offender relationships. In addition, several existing State data sets contain detailed information regarding injuries, weapon involvement, and case processing in the criminal justice system. However, these data sources are only partial indicators of the extent of family violence in Illinois; the data underrepresent the number of individuals who experience violence in their families and households. Illinois currently lacks a single source of comprehensive data on which to base future plans, policy, and services. Information is also unavailable regarding the amount of overlap in the numbers of victims and offenders served by various agencies, the multiple forms of domestic assault occurring within families or households, and other topics. The data quality is unknown as well. Nevertheless, many processes are under way to improve the data. Further strategies to reduce gaps include ensuring that State and local agencies understand the State definition of domestic violence, increasing resources for creating automated systems and improving their capacity, seeking additional family violence data sources as they develop, and other actions. Figures, tables, footnotes, and 23 references