public interface IRecord
{
     int Record_ID { get; set; }
     //Other Properties
}

Class TypeA: IRecord
Class TypeB: IRecord

DataTable TypeARecords
DataTable TypeBRecords

List<IRecord> records; //This may or may not have anything in it, initially.

private void CreateTypeAObjects()
{
DataTable TypeARecords = GetDataMethod();


        foreach (DataRow row in TypeARecords.Rows)
        {
            int recordID = int.Parse(row["Record_ID"].ToString());


            if (records != null && records.Count > 0)
            {
                //If the record is of TypeA and doesn't have an existing object in the collection, create it.
                if ((!records.Where(t => t is TypeA).Any(s => s.Record_ID == recordID)))
                {
                    records.Add(new TypeA
                    {
                        Record_ID = int.Parse(row["Record_ID"].ToString()),
                        //Initialize other properties
                    });

                }
            }
            else
            {
           //If the list is not instantiated, create it now and add record.
                records = new List<IRecord>();
                records.Add(new TypeA
                {
                    Record_ID = int.Parse(row["Record_ID"].ToString()),
                    //Initialize Other Properties

                });
            }

        }
}