I think I have it figured out for you. Lets start with the marriage of your Betsey Ann Horn Married to David Plaisted (family search record) has them Married at Jay, Franklin Maine on 12 Nov. 1854.
I then moved to the 1860 Census records of Phillips, Franklin, Maine where I found David and Betsey ages 33 and 23 respectively children Emma 4, Willis H 3, Charles 1, and Sumner 1/12.
I then moved to the 1870 Census of Avon, Franklin, Maine and found David and Betsey ages 43 and 33 respectively with children Willis 12, Charles 11, Fred 10, and Louisa 8.
Still not knowing who Betsey’s parent were and your note on her death, I looked up in the Maine Death record 1617-1922 on (ancestry.com) and found her record. Betsey A Plaisted, Died 15 May 1898 aged 61 years. In Farmington, Maine. Place of birth is listed as Jay, Franklin, Maine. Parents are listed as Father/Amos Horn and Mother/Dorcus Webber.
Now knowing who her parents are, I checked the 1850 census and found in Jay, Franklin, Maine an Amos and Dorcus Horn ages 36/36 with children Betsey A 11, Charles L 10, John W 7, Hannah O 6, William 4, and unknown 3.
I then found the death record of Dorcus Horn in Maine Death records 1617-1922 (ancestry.com) and her death is listed as 29 Nov 1901 aged 88 yrs 4 mths 29 dys. Born in Lebanon, NH. Spouse of Amos Horn.
I then Found Amos’s death record (same place as before) He died 26 Dec 1906 in Weld, Maine. Birthplace is listed as Fairfield, Maine and Father/ Ichabod Horn, Mother/Ann Webber.
Still not knowing where the Greenfield Horn came from I went to the Franklin County, Maine 1860 and 1870 Census record of Amos and Dorcus and he is listed there as a Son born abt 1851-2. Further research did reveal he married an Leona Thompson. He Died (Maine death records again) on 3 Mar 1912 at Weld, Maine aged 60 yrs 8 mths 20 dys. Son of Amos Horn (birthplace Fairfield, ME) and Dorcus Webber (birthplace Lebanon, NH)
I hope this can shed some light on your research.
Ben, this is absolutely amazing that you found all this. This has been a "dead end " line for me for some time. Wow, I still can't believe it. Thank you so much. This is all the right areas, the right people and my Betsey had children Willis H, Charles, Fred/Ted, and sister Lousia Sydna. You have hit the right buttons for me. How can I thank you? I can't thank you enough.
You're Very Welcome, I just Love this stuff.
I can see you do. I did too when I was younger, and have just posted another query in the forum if you're interested and can find anything for me. Thanks so much, Ben.