Who did the transcription?
If he transcribed the info, then he owns the copyright on that transcription
If he used a published transcription, then the copyright belongs to whoever originally did the transcription
He could always check with whichever dept owns the copyright to the census images to be absolutely sure he isnt infringing
Another point -- is he intending to publish the history? If it is for personal use only, then it probably isnt infringement anyway
Disclaimer : I am not a copyright lawyer, so this maybe wrong