Her death certificate records Mollie Johnson, age 67 years 1 month 26 days, born 1 Jan 1962 in Kentucky, died 26 Feb 1929 at home in Cincinnati, Hamilton Co., Ohio, residence 5711 Madison Rd, widow of Joseph K. Johnson, father Wm Estel, mother’s maiden name unknown, cause of death amyotrophic lateral sclerosis, informant Bain Johnson, burial in Madisonville, Ohio.

The reported birth date is probably too late, perhaps by as much as five years. It would mean that she was married only one month after she turned 13, whereas her marriage record reported her as 18 at that time (and the 1880 census reported her as age 31, which would be a large stretch if she were only 18 then, less of one if she was 22 or 23.)

She may be the Mary Estill age 12 in the following record:

1870 census of Fleming Co., Ky, Poplar Plains precinct, enumerated 24 June, lists on p. 9 as family #58/55:
Estill, Polly, 60, farmer; Mary, 12. Both born in Kentucky.

I cannot find a match in the 1860 census, though.

Fleming Co., Ky marriage records list the marriage on 11 Feb 1875 of Josh K. Johnson, age 33, and Mary Estill, age 18, both born in and residents of Fleming Co., all of their parents born in Fleming Co.

This Johnson family is in my database only to document that their son Frank Lander Johnson is not the same person as the Frank Johnson born 2 Sep 1887 who married Lillie Clark. (Due to their similar birthdates and Ancestry.com’s hinting system, many online family trees confuse the two of them and attach the wrong parents and associated records to Lillie’s husband.)

1880 census of Fleming Co., Ky, Flemingsburg precinct 7, enumerated in June (undated), lists on p. 16 as family #155:
Johnson, Margaret, 67, widowed; Sally, 27, dau, single; Joseph, 37, son, married, farm laborer; Mollie, 31, dau-in-law; Victor, 4, grandson; Nellie, 2, granddau. All born Ky Ky Ky.

The grandson Victor should be a granddaughter Victoria. The age reported here for Mollie is very inconsistent with the marriage record. It reported her as age 18 in Feb 1875, which would make her 23 in June 1880 (or at most 24, if her birthday was between Feb and June.) The 1900 census and her death certificate are inconsistent in the other direction, that is, they report her birth date as Jan 1862, which would make her barely 13 when she married, and 18 in 1880. (This is not a case of Joseph having two wives named Mollie, since the marriage record and death certificate both give Mollie’s maiden name, and the 1900 census gives the number of years married as 25.) I think it is the marriage record that is correct, at least within a year, and that she was really born in 1857 or 1858.

1900 census of Fleming Co., Ky, Flemingsburg precinct, enumerated 2 June, lists on p. 2A as family #30/33:
Johnson, Joseph, 58, b. Nov 1841, peddler of notions; Mollie M., wife, 38, b. Jan 1862, married 25 years, mother of 7 children, 6 living; Margaret K., mother, 85, b. Dec 1814; David L., son, 15, b. Sep 1884; Frank L., son, 12, b. Oct 1887; Charles M., son, 8, b. July 1891; George B., son, 5, b. June 1894. Taylor, Amanda V., dau, 24, b. Dec 1875, married 2 years, 0 children. Walter, Nellie B., dau, 22, b. Feb 1878, married 0 years, 0 children. All born Ky Ky Ky.

1910 census of Hamilton Co., Ohio, Cincinnati ward 16, enumerated 27 April, lists on p. 17B as family #178/456, at 742 Richmond St:
Johnson, Mollie, 49, widowed, mother of 6 children, 6 living; B. Victoria, dau, 30, single, saleslady at dept store; Nell, dau, 27, single, saleslady at dept store; David, son, 25, single, tailor; Charles, son, 19, life insurance agent; Frank, son, 20, motorman for traction co; Benjamin, son, 15, grocery clerk. All born Ky Ky Ky.

Note that both daughters have returned to using their maiden names. Victoria should be 34, and Nellie 32.