I could not figure this one out but here is what I ended up using to find a center point.
private static Point2d generateCentroid(List<clsPoint> lstPoint)
{
double x, y, min_x, min_y, max_x, max_y;
min_x = lstPoint.Min(p => p.X);
min_y = lstPoint.Min(p => p.Y);
max_x = lstPoint.Max(p => p.X);
max_y = lstPoint.Max(p => p.Y);
x = min_x + (max_x - min_x) / 2;
y = min_y + (max_y - min_y) / 2;
Point2d point = new Point2d(x, y);
return point;
}
lstPoint is just a list of the polygon points stored in a class:
public class clsPoint
{
public double X { get; set; }
public double Y { get; set; }
}