Why do some people evaluate state supreme courts as more legitimate than others? Conventional academic wisdom suggests that people evaluate courts in nonpartisan ways, and that people make a distinction between how they evaluate individual court decisions and how they evaluate the court’s legitimacy more broadly. We challenge this idea by arguing that people’s partisan identities have a strong influence on how people evaluate the impartiality of courts, just as they do other aspects of the political world. Using original survey experiments, validated by existing observational survey data, we show that people perceive state supreme courts as being more impartial when courts issue decisions that match the ideological preferences of their preferred political party, while court decisions at odds with their party’s policy goals diminish people’s belief that courts are impartial arbiters of the law. We also show that the effects of citizen perceptions of impartiality erode evaluations of state court legitimacy, which makes them want to limit the independence of judicial institutions.