Both a relationship or a portal filter can be set up to show only records from a selected county and state.
Exactly how you set that up depends on the design of your database.
I tried establishing a filter but I could not get it to work. My formula was "A_SELECT_COUNTY and BIZ UNIT and INVOICE>0" and yet it does not work. Do you have any suggestions?
A_SELECT_COUNTY and BIZ UNIT and INVOICE>0
Makes no sense due to incorrect syntax for a FileMaker calculation. The fields should include a table occurrence name and " ::" before each field name. The and operators are not used correctly either.
What is this expression intended to specify?
What are the tables and relationships involved here? Your layout must refer to one Tutorial: What are Table Occurrences? and your portal must refer to another. The relationship between the two table occurrences then is part of what determines which records are listed in the portal.