Instead of using template checkbox column, you might want to consider using ‘Row Checker’ feature of WebGrid. The IsRowChecker column property allowing you to create efficient multiple rows selection grid interface quickly. There are numerous automated behavior attached when working in this mode, such as select/deselect all checkbox in column header, application of CheckedRowStyle, batch multiple rows selection by pressing Shift key, and much more.

One of the advantages using IsRowChecker column is that it has the behavior to persist row checker during PostBack in WebGrid. This makes the row checker is not being cleared during postback.

The step-by-step below shows how to create IsRowChecker column and enable its PersistRowChecker feature.

Adding RowChecker column in WebGrid

1. Bind WebGrid to the data source.
2. Set WebGrid’s properties AllowEdit to True.
3. Right-click on WebGrid and click on WebGrid.NET designer.
4. Go to Advanced tab – RootTable – Columns
5. Click Add (to add a new column).
6. Set focus to Layout expandable panel, checked “Is row checker column” checkbox.
7. Click Apply and OK.
8. The picture will look like the following.
   
9. The WebForm will look like the following snapshot:
   

<Columns>
    <ISWebGrid:WebGridColumn Name="WebGridColumn0" Width="100px" IsRowChecker="true">
    </ISWebGrid:WebGridColumn>
    ...
</Columns>

Persist row checker during PostBack

1. Open WebGrid.NET Designer.
2. Focus on Popular Settings and click See all properties.
3. Set PersistRowChecker to True in Advanced – WebGrid – LayoutSettings.

<LayoutSettings AllowEdit="Yes" AllowSelectColumns="Yes" PersistRowChecker="true">
</LayoutSettings>

Hope this helps.