const int MaxEntriesInBook = 200;
var employees = Enumerable.Range(0, 601).ToList();
double d_empCount = (double)employees.Count;
List<Book> books = new();
int booksAmount = (int)Math.Ceiling(d_empCount / MaxEntriesInBook);

int employeeIndex = 0;
for (int i = 0; i < booksAmount; i++)
{
    double employeesPerBook = Math.Ceiling(d_empCount / booksAmount);

    int employeesToTakeAmount =
        employees.Count - employeeIndex > MaxEntriesInBook
        ? (int)employeesPerBook
        : employees.Count - employeeIndex;

    var employeesToTake = employees.GetRange(employeeIndex, employeesToTakeAmount);
    books.Add(new Book() {Employees = employeesToTake});
    employeeIndex += employeesToTakeAmount;
}

books.Select(b => b.Employees.Count).Dump();
books.Sum(b => b.Employees.Count).Dump();

class Book
{
    public List<int> Employees { get; set; } = new();
}