Gridviews can be created dynamically.
Use the Placeholder
control[
^] and create a placeholder on the design page.
Then add gridview controls to this placeholder on demand (based on number of entries in the text box).
E.g.
for(int i=0; i++, i<= numCount)
{
GridView gv = new GridView();
gv.ID = "_gridview" + i;
placeholder1.Controls.Add(gv);
}
Set the data source of the grid views as required.