Methods, apparatus, and systems are disclosed to correlate census measurement data with panel data. An example system includes accessing means to access a message sent from a requesting device in response to accessing media that includes a tag causing the requesting device to send the message to a monitoring entity with an identification of a geographic location of the requesting device and media identifying information. The example system also includes identification means to determine locations of a plurality of panelist homes and compare the geographic location of the requesting device with the locations of the panelist homes. The example system also includes associating means to identify a user of the requesting device as a panelist residing at the first panelist home and associate the media identifying information with panelist data associated with the first one of the panelist homes.