The Internet of Things (IoT) has potential to deliver important benefits for IoT users, society and public good. How do citizens feel about sharing data from personal devices compared with “smart city” data collection in public spaces, with government and nongovernmental organizations, and across different situations? What predicts willingness to share their data with government? Through a nationally representative survey of over 2000 US respondents as well as interviews, we explore the willingness of citizens to share their data in various circumstances, using the contextual integrity framework, the literature on the “publicness” of organizations, and public value creation. Across different contexts, from half to 2/3 of survey respondents were willing to share data from their own IoT devices for public benefits, and 80%−93% supported the use of sensors in public places for a variety of collective purposes. Trust in government was significantly related to data sharing and support for smart city data collection. Yet government in the United States is less trusted with this data than other organizations with public purposes, such as nonprofits. Cultivating trust through transparent and responsible data stewardship will be important for future use of IoT data for public good.