Get the Data in DataTable and using for loop you can add the Row cell values to List of String.
Please refer this code
C#
string constr = ConfigurationManager.ConnectionStrings["constr"].ConnectionString.ToString();
List<string> list1 = new List<string>();
using (SqlConnection con = new SqlConnection(constr))
{
using (SqlCommand cmd = new SqlCommand("select FirstName from Employees", con))
{
SqlDataAdapter da = new SqlDataAdapter(cmd);
DataTable dt = new DataTable();
da.Fill(dt);
for (int i = 0; i <= dt.Rows.Count - 1; i++)
{
list1.Add(dt.Rows[i]["FirstName"].ToString());
}
}
}
VB.Net
Dim constr As String = ConfigurationManager.ConnectionStrings("constr").ConnectionString.ToString()
Dim list1 As New List(Of String)()
Using con As New SqlConnection(constr)
Using cmd As New SqlCommand("select FirstName from Employees", con)
Dim da As New SqlDataAdapter(cmd)
Dim dt As New DataTable()
da.Fill(dt)
For i As Integer = 0 To dt.Rows.Count - 1
list1.Add(dt.Rows(i)("FirstName").ToString())
Next
End Using
End Using