Count a subset of records in a query

I am trying to place a footer on a form which counts a subset of the records
that the form displays based on one of its fields. The form uses a query to
display its data which is extracted from company mainframe and updated
nightly. The query and forms break down the data by day and workgroup. I want
to be able to display the number of records counted by one of its fields
which is a drop down list and restricts user to a limited number of
selections.