Use RectangleGeometry as Path Data
<UserControl x:Class='SilverlightApplication3.MainPage'
xmlns='http://schemas.microsoft.com/winfx/2006/xaml/presentation'
xmlns:x='http://schemas.microsoft.com/winfx/2006/xaml'
xmlns:d='http://schemas.microsoft.com/expression/blend/2008'
xmlns:mc='http://schemas.openxmlformats.org/markup-compatibility/2006'
mc:Ignorable='d'
d:DesignWidth='640'
d:DesignHeight='480'>
<Path Stroke="Black" StrokeThickness="1" Fill="#CCCCFF">
<Path.Data>
<RectangleGeometry Rect="30,55 100 30" />
</Path.Data>
</Path>
</UserControl>
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