Mecham
A surname most likely developed as a spelling of Meacham, a name tied to a place-name or an old personal-name form.
The #8,356 most common surname in the United States (2010 Census) — about 1 in every 77,927 Americans shares it.
Etymology
The historical source you provided treats Mecham as a variant of Meacham rather than a separate origin. Meacham is generally understood as an English surname that can go back to a place-name or, in some cases, to a personal-name formation in early English. The exact root is not certain from the excerpt alone, so the safest reading is that Mecham is an English surname arising through spelling variation.
History
Lower’s dictionary explicitly cross-references Mecham to Meacham, showing that the two names were already being treated as variants in the 19th century. The modern U.S. spelling Mecham is less common than Meacham, but it follows the same pronunciation pattern. In American records, such spellings often stabilized independently in different branches of a family.
Origin
Regions
Variant spellings
Fun fact
19th-century surname dictionaries often treated short spellings like Mecham as simple variants rather than distinct surnames, which is exactly how this name is handled in the source excerpt.
From the historical record
“calfe. MECHAM. See Meacham. INIECHAXT. Fr. Bad, wicked. ^lEDCALF. See ^letcalfe. IMEDES. The same as Meads. MEDHURST. Probably either Mid- hurst or Madehurst, both parishes in Sussex. De Medhurst. H.R. co. Kent.”
— Patronymica Britannica: a dictionary of the family names of the United Kingdom