This paper addresses the question, “how effective are Illinois counties in converting wealth (GDP) into wellbeing of residents”. To address this question, a multi-item measure of wellbeing (SEDI) was constructed using publicly available data. Based on the multi-item measure, a wellbeing development index (WDI) was calibrated for each county. The SEDI and its derivative the WDI are relative measures, they highlight how a county performs relative to the entire universe of Illinois counties or individual peer groups (for example, economic development regions).To facilitate adaption of SEDI, a software is provided free for practitioners interested in assessing the wellbeing status of Illinois counties.