Confident, with your help, that have the right Jane Thomas (nee Stone) 1900 onwards (emigrated around the right time and has Robert Zimmer, son of her daughter Mary with her in 1900 and other daughter Harriet with her (as Lawrence) in 1910) and that it is her and John Thomas in the 1880 census (with Harriet and Mary and also son Thomas who we know is the son of John C Thomas and Jane Stone).
Struggling to find the correct John C. Thomas (her husband) in later census. Unfortunately the 1890 census does not exist and John in 1900 census is a best guess.
In 1900 Jane is listed as divorced and in 1910 as widowed, therefore the grave of John C Thomas born 08 Oct 1841 and died 08Jan1907 seems to fit nicely. However confusingly on this gravestone are:
William C Thomas: 16Mar1867 to 08Jul1923 and
Alice N. Thomas: 10Aug1868 to 11Jul1924
Their years of birth would indicate they are children of John and therefore you would expect them to be with him in the 1880 census. Alice is not and although there is a William with him in 1880, his birth year is 1869, close but close enough? Therefore is this him?
Have tried looking for Alice N, William C and John C Thomas separately or together in BMD and census but with no obvious luck. Perhaps those with better skills than mine can?
Jane is listed as divorced in 1900 therefore John C could easily be with another wife between 1880 and 1900, which doesn't help things.
The only possible candidate
I can find for John C in 1900 (other than the one previously discounted is further on below) is this one. His status is widowed which at first glance means he could not be Jan's husband as she is alive and divorced in 1900. However, if he was divorced in the intervening years he could easily have remarried and "widowed" might refer to his second wife?
A John C. Thomas, born 1840 Wales in the 1900 census is below
https://www.familysearch.org/ark:/61903/3:1:S3HT-6SG3-Y2N?i=32&cc=1325221Name John C Thomas
Event Type Census
Event Year 1900
Event Place Trimble Township Trimble village, Athens, Ohio, United States
Gender Male
Age 60
Marital Status Widowed
Race White
Race (Original) W
Relationship to Head of Household Boarder
Relationship to Head of Household (Original) Boarder
Birth Date 1840
Birthplace Wales
Father's Birthplace Wales
Mother's Birthplace Wales
Living with
Andrew Johnson Head M 40 Ohio
Lizzie Johnson Wife F 38 Ohio
John C Thomas Boarder M 60 Wales
The below we have previously discounted
(Jane found living separately in 1900, this pair emigrated in early 1860)
Other (1) John C. Thomas (1900)
https://www.familysearch.org/ark:/61903/3:1:S3HT-6SG3-BFM?i=20&cc=1325221Name John C Thomas
Event Type Census
Event Year 1900
Event Place Athens Township (incl. Athens Insane Asylum), Athens, Ohio, United States
Gender Male
Age 54
Marital Status Married
Race White
Race (Original) W
Relationship to Head of Household Head
Relationship to Head of Household (Original) Head
Years Married 28
Birth Date Oct 1846
Birthplace Wales
Marriage Year (Estimated) 1872
Immigration Year 1861
Father's Birthplace Wales
Mother's Birthplace Wales
John C Thomas Head M 54 Wales
Jane Thomas Wife F 59 Wales
William Thomas Son M 20 Ohio
Thomas Thomas Son M 24 Ohio
Celia Evens Granddaughter F 13 Ohio
The below John C Thomas can also be discounted as he is alive in 1910 census and is also in 1880 census with same family, different wife and emigrated 1866 when Jane was still in Wales
Other (2) John C. Thomas (1900)
https://www.familysearch.org/ark:/61903/3:1:S3HT-D4G7-1W5?cc=1325221Name John C Thomas
Event Type Census
Event Year 1900
Event Place Steubenville Township Mingo Junction village, Jefferson, Ohio, United States
Gender Male
Age 56
Marital Status Married
Race White
Race (Original) W
Relationship to Head of Household Head
Relationship to Head of Household (Original) Head
Years Married 34
Birth Date Dec 1844
Birthplace Wales
Marriage Year (Estimated) 1866
Immigration Year 1872
Father's Birthplace Wales
Mother's Birthplace Wales
John C Thomas Head M 56 Wales
Thomas Wife F 58 Wales (wife is Mary from other census entries)
Edward F Thomas Son M 33 Wales
Isaac Thomas Son M 26 Wales
Elizabeth Thomas Daughter F 24 Ohio
Ruth Thomas Daughter F 22 Ohio
Llueellyn Thomas Son M 28 Ohio (Llewelyn)
Annabelle Thomas Daughter F 20 Ohio