ORDER BY in SQL query Error: syntax error near the word WHERE

I tried to show the most recent activity performed on user's account but I am getting an error that says:

syntax error near  the word 'WHERE'

string connectionString = ConfigurationManager.ConnectionStrings["ConString"].ConnectionString;
using (SqlConnection con = new SqlConnection(connectionString))
{
    using (SqlCommand cmd = new SqlCommand("SELECT * FROM ActivityTable ORDER BY ActivityDate DESC WHERE ActivityBy =@ActivityBy", con))
    {
        cmd.Parameters.AddWithValue("@ActivityBy", byuser.Text.Trim());
        con.Open();
        SqlDataReader dr = cmd.ExecuteReader();
        if (dr.Read())
        {
            activitylbl.Text = dr["ActivityDetail"].ToString();
        }
        else
        {
            activitylbl.Text = "No activity on this account";
        }
        con.Close();
    }
}