Looking for my 3rd Great Grandmothers Parents

Hi,

Does anyone have an Ida Cox on your Family tree? Who was born in Plymouth IL (Says on her death certificate) on Aug 9th 1869 (says on the 1900 Census) or on Aug 9th 1877 (Says on her death certificate) and Died in Saint Louis, Mo on Aug 9th 1928 of Brites disease.

She was supposedly full-blooded Cherokee and her father was William Cox. I still don’t know her mother’s name, and I am still looking to find that out? I am not really 100% sure William was her father.
Around the age of 14 she married a white man named George W. Green and where married in 1885 in Pike County MO, her father was there and was present and have his consent.

They had 6 children together:

Charles Green 1886 –
Bridie Green 1890 –
Frank Green 1891 –
Maudie Green 1892 –
Dolly Green 1894-
Inez Green 1899 –

Then she something happened to George and then she met my 3rd Great Grandfather Theodore Dowell and had 2 children a boy and a girl. Velma is my 2nd Great Grandmother.

Harry Dowell 1904 – 1944
Velma Dowell 1906 – 1975

Then she married a man named Manning Miller who died in 1918 and the remarried again to a man named Frank Martin. Then she died in 1928 in Saint Louis City, MO.

Also on the 1900 Census she listed as her mother and father born in IL and the family says after Ida was born, they moved to the CN in Oklahoma. And after she ran away, the family moved to the Saint Louis area. It is also said that her and her mother and father had Native names, but no one knows what they were and I think she had a few siblings. But the only one I found was Maud Cox- 1890-Missouri. In the 1910 census it list Maud at the age of 19 and she is the sister in law to Manning Miller. It listed her as Maud Shild and I assume her sister is Ida Miller, (my 3rd Great Grandmother), Ida had a daughter from a previous marriage and list her as Velma Miller age 3.

Ida and her sister Maud list both of their parents as being born in Illinois. So if anyone could look up any info about Maud to confirm that Ida is her sister and who her parents name are I would appreciate. All I know that Ida’s father is William Cox so I am assuming that Maud is also his daughter.

If you have any info that can help with this task of finding documentation of Ida and her parents being Native, I would appreciate it.

BTW Ida Cox is my 3rd Great Grandmother and is Full-Blooded Cherokee and Theodore Dowell is my 3rd Great Grandfather and Velma Dowell is my 2nd Great Grandmother.

Where there any Cherokee people living in IL at the time of her Birth? Also, she in the 1903 Saint Louis New paper listing her and her children of having the measles and a family of 7 living on 4 dollars per week , she is still known by Mrs. Green at the time.