void Application_Start(object sender, EventArgs e) 
{
     Application["NoOfVisitors"] = 0;
}
void Session_Start(object sender, EventArgs e) 
{
    Application.Lock();
    Application["NoOfVisitors"] = (int)Application["NoOfVisitors"] + 1;
    Application.UnLock();
}
now aspx page
<table>
            <tr>
                <td>
                    <b>No of Visits:</b>
                </td>
                <td>
                    <asp:LabelID="lblCount"runat="server"ForeColor="Red"/>
                </td>
            </tr>
        </table>

now aspx.cs page

lblCount.Text = Application["NoOfVisitors"].ToString();