In the field of health services research, many secondary data sets exist that can be aggregated to higher order units of analysis to examine trends in the structure of the health care marketplace. In particular, the American Hospital Association Annual Survey includes organizational characteristics of hospitals in the United States. However, hospital systems—defined as groupings of hospitals within a delineated organizational structure—play an outsized role in the health care landscape, and as a result, are important entities to study. Unfortunately, there are limited data available at the hospital system level. This case study provides an overview of the process of aggregating the hospital-level data to the system level. The process requires careful attention to data harmonizing and cleaning prior to aggregation to ensure that the aggregation does not magnify errors in the data. This case will discuss the data harmonizing and aggregation processes and provide suggestions to validate the data, as well as describe approaches to augment the panel data with additional secondary sources. This case study will help readers identify opportunities to leverage secondary data sets with hierarchical units of observation that can be aggregated to higher levels of analysis.