Hi, following in your footsteps from the 1860/1870 censuses, I think John died between 1870-1880.

Here's what I'm seeing.

*United States Census, 1860
Name: Charlotte Harris
Event Type: Census
Event Year: 1860
Event Place: Union Township, Ross, Ohio, United States
Gender: Female
Age: 6
Race: Mulatto
Race (Original): Mulatto
Birth Year (Estimated): 1854
Birthplace: Virginia
Household Role Gender Age Birthplace
John Harris M 50 Virginia
Martha Harris F 40 Virginia
Victoria Harris F 10 Virginia
Rufus Harris M 8 Virginia
Charlotte Harris F 6 Virginia
James Harris M 4 Virginia
John Plum M 19 Virginia
Henry Harris M 45 Virginia

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*United States Census, 1870
Name: Charlotte Harris
Event Type: Census
Event Year: 1870
Event Place: Zenia, Greene, Ohio, United States
Gender: Female
Age: 19
Race: Mulatto
Race (Original): M
Birth Year (Estimated): 1850-1851
Birthplace: Virginia
Page Number: 21
Household Role Gender Age Birthplace
John Harris M 47 Virginia
Martha Harris F 46 Virginia
James Harris M 17 Ohio
Charlotte Harris F 19 Virginia

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Their son Rufus from the 1860 census is living next door to them.

*United States Census, 1870
Name: Rufus Harris
Event Type: Census
Event Year: 1870
Event Place: Zenia, Greene, Ohio, United States
Gender: Male
Age: 21
Race: Mulatto
Birth Year (Estimated): 1848-1849
Birthplace: Virginia
Page Number: 21
Household Role Gender Age Birthplace
Rufus Harris M 21 Virginia
Elizabeth Harris F 19 Kentucky
Lewis Harris M 0 Ohio

https://familysearch.org/pal:/MM9.3.1/TH-267-11598-96151-18?...

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In the 1880 census Charlotte is married to a David Lee. He mother Martha is living with them and listed as widowed. I assume John died between 1870-1880 Zenia, Ohio.

*United States Census, 1880
Name: Martha Harris
Event Type: Census
Event Year: 1880
Event Place: Xenia, Greene, Ohio, United States
Gender: Female
Age: 55
Marital Status: Widowed
Race: Mulatto
Race (Original): MU
Occupation: At Home
Relationship to Head of Household: Mother-in-law
Relationship to Head of Household (Original): MotherL
Birth Year (Estimated): 1825
Birthplace: Virginia, United States
Father's Birthplace: Virginia, United States
Mother's Birthplace: Virginia, United States
Affiliate Publication Number: T9
Affiliate Film Number: 1020
Household Role Gender Age Birthplace
David Lee Self M 30 North Carolina, United
Charlotte Lee Wife F 26 Virginia, United States
Martha Harris Mother-in-law F 55 Virginia, United States

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I'm guessing Martha died before 1900. In the 1900 census Charlotte is still married to David Lee and with no children. It was quite common back then for the mother to stay with her youngest daughter, if she became a widow.

*United States Census, 1900
Name: Lottie Lee
Event Type: Census
Event Year: 1900
Event Place: Xenia Township Xenia city Ward 4, Greene, Ohio, United States
Gender: Female
Age: 48
Marital Status: Married
Race: Black
Relationship to Head of Household: Wife
Number of Living Children: 0
Years Married: 27
Birth Date: Jan 1852
Birthplace: Virginia
Marriage Year (Estimated): 1873
Father's Birthplace: Virginia
Mother's Birthplace: Virginia
Mother of how many children: 0
Household Role Gender Age Birthplace
David Lee Head M 59 North Carolina

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Hope this helps