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OK - mystery solved. Milton C. Lighter was a son of Edwin Nathanil Lightner and Sarah Ellis. Edwin Nathaniel Lighter was a brother of the other Milton Clarkson Lightner, so your Milton Clarkson Lightner was named after his 'uncle' (his father's brother). Edwin Nathanial Lightner was born about 1816 and is in the August 1850 Upper Merion, Montgomery, Pa census. Given that this census was taken in August and that Milton Jr. was born in Dec of the same year, I would gather he was born in Montgomery county. This family, now with M.C. Lightner, aged 10, is then found in the 1860 Danvile, Montour, Pa census. Edwin Nathanial Lightner is also an episcopal clergyman.
So there you have all the facts, verified by Milton Jr's own Turnley grandfather and confirmed by all the censuses. Edwin Nathaniel Lightner's father was Nathaniel Ferree Lightner. Your line goes all the way back!