Death Certificate of Lewis Gardner Blackwell shows his father as Robert Blackwell born Hackettstown NJ.
1850 Census Lewis Gardner Blackwell says he was born in NJ. So Robert Blackwell was still in NJ in 1825.
In 1850 Robert Blackwell is living in NJ in the Taylor Household with apparently his daughter - he is no longer on the NJ Census or the Pa Census in 1860. Need to Check Stephensberg - that's where the Taylor household was.
Was living in Allamuchy NJ in 1839 when Executors of Elijah Blackwells will transferred his real estate. Book 18, pages 59, 60, 61, nd 62, Warren Co., NJ, book of deeds. Obit of Lewis G. Blackwell suggests that Robert went back to NJ - after Sarah Ann Gardner Blackwell died circa 1833 (calculated from Obit of Sarah Ann Blackwell Taylor)