Stereotypes are often used to make inferences about others, yet can lead to problematic consequences, which get exacerbated when people are more confident in these inferences. The current research examines whether biases in people’s first-hand and second-hand information about groups make groups appear overly homogeneous, leading to more confident inferences about group members. Supporting this, across two studies, groups appeared more homogeneous when people lacked first-hand information from personal experience with a group, and when stereotypes were based on second-hand information from the media or other people. However, only second-hand information increased confidence about group members, as lacking first-hand information reduced confidence about what groups and group members were like. Biases in homogeneity also had greater impact for typical rather than atypical group members. Thus, people may be especially confident in stereotype-based inferences when stereotypes are based on second-hand information, and when group members appear typical of their group.