It feels like the DataGrid is holding onto the type "assigned" from the DataTable but I am not sure.AFAIK, you cannot change the Datatype of a Datagridview Column after it's created. You'd have to instead create a new column with your desired type, and fill it as needed. You can set the Column DataPropertyName to the column in your underlying dataset, and the grid should show the values in that column (assuming they're compliant with the column's datatype, of course).