How do I set the width of a column in my DataGrid

To set a column width, your datagrid must be using a non-null DataGridTableStyle. Once this is in place, you can set the column width by first
getting the tablestyle and then using that object to obtain a column style with which you can set the width. Here are some code snippets showing
how you might do this.

//.... make sure your DataGrid is using a tablestyle
dataGrid1.DataSource = _dataSet.Tables['customers'];
DataGridTableStyle dgts = new DataGridTableStyle();
dgts.MappingName = 'customers';
dataGrid1.TableStyles.Add(dgts);

//......

//method to set a column with by colnumber
public void SetColWidth(DataGridTableStyle tableStyle, int colNum, int width)
{
	try
	{
		tableStyle.GridColumnStyles[colNum].Width = width;
		tableStyle.DataGrid.Refresh();
	}
	catch{} //empty catch .. do nothing
}

//....

// here is how you might call this method

private void button1_Click(object sender, System.EventArgs e)
{
	DataGridTableStyle tableStyle = dataGrid1.TableStyles['customers'];
	SetColWidth(tableStyle, 1, 200);
}