Check on "cascading combo boxes" -- this is the term used to describe when
combo box1 is used to limit what's shown in combo box 2, and cb2 limits
cb3...

The most efective way that I used

On the RowSource of combo 2 build a criteria that refer to
the field of combo 1, and from combo 3 a criteria to combo
2, etc

You'll need just a little VBA code to do this.

I gather downthread that you have a table of Regions and Counties.
Base the first combo, cboRegion say, on a query selecting just
Regions, using the "Unique Values" property of the query. The SQL
would be something like

SELECT DISTINCT Region FROM AreaTable ORDER BY Region;

Create a second query to select the counties, *using the first combo
box as a criterion*. It will be something like

SELECT County FROM AreaTable
WHERE AreaTable.Region = Forms!YourFormName!cboRegion
ORDER BY County;

Base a new combo box, cboCounty, on this query. Then Requery the
county combo in the AfterUpdate event of the Regions combo. View the
combo's properties, and on the Events tab click the ... icon by the
AfterUpdate event; choose the Code Builder; and enter

Private Sub cboRegion_AfterUpdate() ' Access gives you this free
Me!cboCounty.Requery
End Sub                             ' and this as well

                 John W. Vinson[MVP]