There are several ways to modify the ChartLegend content.
The first is to manually create the legend items, like demonstrated in this
You can also try using the LayoutUpdated event to change the already present content:
sender, EventArgs e)
//Do not forget to unsubscribe, or you will cause a Layout Cycle
"Count of "
But perhaps the easiest one is set the the LegendLabel
property of the series definition to the string you want to have in the corresponding legend item.
If you have any further questions feel free to ask.
the Telerik team