In the 1850 Census I found Elijah again, this time in Hadley, Hampshire, MA: Elijah H. Bartlett 34MA Charlotte S wife 34 Levi 9 Henry F (Frank?) 3
He was living next to his parents Levi and Dorinda Bartlett.
On my previous post I said Mary was E. H. Bartlett's first wife, but that seems to be incorrect. His first wife was actually Charlotte Smith Cook Bartlett, 1813-1860. Mary was another of E. H's relatives, poss. a sister.
Check the "Hockanum Cemetery" Hampshire County site (use quotations when you search) to see a list of the Bartletts buried there. Elijah Henry Bartlett's father definitely is Levi Bartlett, 1783-1839, and his grandparents most likely were John Bartlett, 1744-1829, and his wife Elizabeth.