Flex align checkbox in datagrid Flex

Instead of using <mx:Box />, use <mx:Canvas /> or <s:Group /> (in Flex 4).

Also, set the horizontalCenter="0" on the checkbox.

For example:

<mx:itemRenderer>
    <mx:Component>
        <mx:Canvas width="100%" height="100%">
            <mx:CheckBox selected="{data.visibleInd}" horizontalCenter="0" />
        </mx:Canvas>
    </mx:Component>
</mx:itemRenderer>

Simply use DataGridColumn's textAlign Style:

<mx:DataGridColumn headerText="Visible" textAlign="center">
    <mx:itemRenderer>
        <mx:Component>
            <mx:CheckBox selected="{data.visibleInd}"/>
        </mx:Component>
    </mx:itemRenderer>
</mx:DataGridColumn>