It has been a while since I've mentioned Clark and Mary (Dingman) Sargent in Casefile Clues.
The 1890s genealogy of the Sargent family indicated that Clark died in Winnebago County, Illinois, a statement that is repeated in various other genealogies of the family, a few New England town histories, and countless websites. There are no vital records that early in Illinois--so primary information from original sources will be difficult to obtain.That he died before Mary Married Asa Landon in the 1850s seemed reasonable.
Readers may remember that their daughter, Emmar, gave extensive testimony in her widow's Civil War pension application, including a few details about her birth and early life. Her testimony seems to infer that her father left the family in the 1840s instead of dying.
Which means that Mary might have divorced Clark. And that means another record to look for.
Emmar might have been incorrect about her father "leaving" but a search for a divorce is still in order.