Conventional wisdom holds that much if not most innovation comes from startup companies. But patent records don't say much about the owner/assignee aside from name & location. Publicly-trade assignees have been matched to Compustat, but only 5% of assignees are publicly traded. We provide a dataset that reports the founding year of U.S.-based assignees for 85% of patents from 1976-2021. We also match assignees to PitchBook and include a flag for whether the assignee ever raised venture capital. More details can be found at https://foundingpatents.com.