Before the 15th amendment was adopted, black suffrage was decided by state referenda. There were a total of 27 in all the states and territories. Before the US 15th amendment was adopted, only one state (Minnesota) and one territory (the Dakotas) adopted black (male only) right to vote. Michigan did not adopt this right till its 3rd referendum after the US 15th amendment is adopted. Prior Michigan referendum attempts occurred in 1850 and 1868. Black women gained suffrage in 1909 with the passage of the 19th amendment (women’s suffrage).
Reference: The African American Electorate, By Hanes Walton, Sherman C. Puckett, Donald R. Deskins, CQ Press/SAGE Publications, 2012.
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