Hi simflex,

Please refer below sample.

HTML

UserControl

<table>
    <tr>
        <td>
            Enter State
        </td>
        <td>
            State ID
        </td>
    </tr>
    <tr>
        <td>
            <asp:TextBox ID="txtState" runat="server" />
        </td>
        <td>
            <asp:TextBox ID="txtStateId" runat="server" />
        </td>
    </tr>
</table>

Default

<asp:ScriptManager ID="sm1" runat="server" />
<asp:UpdatePanel ID="up1" runat="server">
    <ContentTemplate>
        <div class="demo">
            <table>
                <tr>
                    <td>
                        <asp:PlaceHolder ID="ph1" runat="server" />
                        <br />
                        <asp:DropDownList ID="ddlCountries" runat="server" OnTextChanged="ddlCountries_TextChanged" AutoPostBack="true">
                            <asp:ListItem>--select--</asp:ListItem>
                            <asp:ListItem>1</asp:ListItem>
                            <asp:ListItem>2</asp:ListItem>
                            <asp:ListItem>3</asp:ListItem>
                            <asp:ListItem>4</asp:ListItem>
                        </asp:DropDownList>        
                    </td>
                </tr>
            </table>
        </div>
    </ContentTemplate>
</asp:UpdatePanel>
<br />
<asp:Literal ID="ltlCount" runat="server" Text="0" Visible="false" />
<asp:Literal ID="ltlRemoved" runat="server" Visible="false" />
<br />
<br />
<asp:GridView runat="server" ID="gvInsertedRecords" />

Namespaces

C#

using System.Data;
using System.Data.SqlClient;
using System.Configuration;

Code

UserControl

public event EventHandler RemoveUserControl;

protected internal void btnRemove_Click(object sender, EventArgs e)
{
    RemoveUserControl(sender, e);
}

Default

protected void Page_Load(object sender, System.EventArgs e)
{
    if (!this.IsPostBack)
    {
        AddAndRemoveDynamicControls();
    }
}
protected void ddlCountries_TextChanged(object sender, EventArgs e)
{
    ltlCount.Text = ddlCountries.SelectedValue;
    AddAndRemoveDynamicControls();
}

private void AddAndRemoveDynamicControls()
{
    int ControlID = 0;
    ph1.Controls.Clear();
    if (!this.IsPostBack)
    {
        UserControl DynamicUserControl = (UserControl)LoadControl("UserControl.ascx");
        ControlID += 1;
        DynamicUserControl.ID = "uc" + ControlID;
        ph1.Controls.Add(DynamicUserControl);
    }
    for (int i = 0; i <= (Convert.ToInt16(ltlCount.Text) - 1); i++)
    {
        UserControl DynamicUserControl = (UserControl)LoadControl("UserControl.ascx");
        while (InDeletedList("uc" + ControlID) == true)
        {
            ControlID += 1;
        }

        DynamicUserControl.ID = "uc" + ControlID;
        ph1.Controls.Add(DynamicUserControl);
        ControlID += 1;
    }
}

private bool InDeletedList(string ControlID)
{
    //Determine if the passed in user control id has been stored in the list of controls that were previously deleted off the page
    string[] DeletedList = ltlRemoved.Text.Split('|');
    for (int i = 0; i <= DeletedList.GetLength(0) - 1; i++)
    {
        if (ControlID.ToLower() == DeletedList[i].ToLower())
        {
            return true;
        }
    }
    return false;
}

public Control GetPostBackControl(Page page)
{
    Control control = null;

    string ctrlname = page.Request.Params.Get("__EVENTTARGET");
    if ((ctrlname != null) & ctrlname != string.Empty)
    {
        control = page.FindControl(ctrlname);
    }
    else
    {
        foreach (string ctl in page.Request.Form)
        {
            Control c = page.FindControl(ctl);
            if (c is System.Web.UI.WebControls.Button)
            {
                control = c;
                break;
            }
        }
    }
    return control;
}