Update: 8 Oct 2014:
I decided to take a thorough inventory of Keen families in the Sumner area between 1800 and 1820 when Abigail married Peres. I eliminated a few families and then I came to Zadoc Keen. He married his first wife in 1797 and married again about 1802. That was a tantalizing window. But I couldn’t find any other information about the first marriage or whether his first wife, “Rebecca Marthers” died. I posted on Chris Dunham’s Maine Genealogy site, and a few hours later Chris worked his magic:

“It's rare that I can find one document that proves several hard-to-establish links at once, but I think I have.

If you go here (https://i2a.uslandrecords.com/ME/OxfordEast/D/Default.aspx), change the Search Criteria to "Early Books" and search for volume 14, page 396 you'll find an agreement dated 23 Aug. 1804 between John Mathews of Buckfield and Zadock Keen of Sumner. For the consideration of one yoke of oxen, Mathews agreed to keep Nancy Keen, the daughter of Zadock, until she was 18 years old, which would be on 5 April 1815. Mathews was "Also to deliver to the said Nancy & Abigail Keen all the clothes & household goods in his possession at the end of such term, that belonged to their Mother Rebeckah Keen of Sumner deceased.

“So it appears that Zadoc and Rebecca (Mathews) Keen had at least two children: Nancy, born 5 April 1797; and Abigail. Abigail (Keen) Andrews is buried in Redding Cemetery in Sumner. She died 4 Oct. 1856, aged 58 years, 1 month, 14 days, which puts her date of birth at about 20 Aug. 1798. Her sister was quite possibly the Nancy Keen who married Nathaniel Robbins, Jr., 9 Mar. 1823 in Sumner. Both were of Plantation No. 2, also called Franklin Plantation, which then adjoined Sumner.

“I transcribed early Turner marriage records several years ago, and according to my notes Zadock Keen of Hebron and Rebeca Marthers of Buckfield married 19 July 1796. Rebecca was evidently the daughter of John and Hannah Mathews of Buckfield, though she is not listed among their children in the History of Buckfield (probably because she died at a fairly young age):

“John Matthews, a Revolutionary soldier, with wife, Hannah, settled in the s. e. part of the town before 1800. They came here from the vicinity of Portland. We have no dates of their deaths, children all born before coming here: Valentine, b. Sept. 3, 1767, m. Sarah Coburn ; Hannah, b. Mar. 9, 1770, m. Jonas Coburn; Lucy, b. Aug. 15, 1773; John, Jr., b. Aug. 23, 1777; Samuel, b. June 22, 1779 ; Caroline, b. Aug. 7, 1782 ; Wm. b. Mar. 29, 1784, m. Eliza Buck.”

Thanks again, Chris! The search continues for more details.

Nathaniel, Nancy and James and Angelia (Robbins) Andrews family listed on 1860 USC for Omro, Winnebago Co., WI.

Is she the widowed pauper Nancy Robbins in the poor house in Woodstock, ME, at time of 1880 USC?