In the 1990s and 2000s, Illinois joined many American states in deregulating its electricity markets to create new, cheaper options for residential customers. Despite this, a competitive retail electricity market has not emerged in Illinois, where incumbent utility companies continue to supply lower-priced electricity than the Alternative Retail Electricity Suppliers (ARES) that were supposed to compete with them. I will draw from government statistics, expert interviews, and public documents to explain why ARES struggle to compete with incumbent utility companies and why some customers choose to switch to ARES despite the often higher prices. I will demonstrate that the incumbent utility companies’ price advantage over ARES results from conditions in the energy market over the past decade, not from an inherent feature of Illinois’s retail electricity market. In a country without a consensus on energy market deregulation, where different states have deregulated their energy markets to vastly different degrees, case studies such as this one help reveal how an individual state’s combination of policies affects ordinary customers.