Control the sort order of a lookup columns

Lookup field values inherit their sort order and filtering from the default view of the lookup list.

If you need to change the sort order of items that appear in a drop-down that is fed from a list in the site you simply need to modify the default view of the SharePoint list containing the lookup values.

You simply need to add a new column to the lookup list and modify the default view in this list as follows:

1. Add a number field to the list naming it "SortOrder" (we used the name SortOrder but you can name it as you wish)
2. Edit the default view of the list to sort by the "SortOrder" column you created in step 1
3. Finally, set the SortOrder value of each item in the list to determine the order they appear in the dropdown.