Using COALESCE And Retrieving Data

I'm preparing a report that will display provider number, provider name, and a single field that will show all the counties that specific provider serves. I realize from researching the coalesce posts that this can be done. However, when I try to retrieve data in the same select statement as my coalesce, I get the error: "A SELECT statement that assigns a value to a variable must not be combined with data-retrieval operations."The listing of the counties must be specific to the provider, so my original code was:

DECLARE @Counties varchar(1000)
SET @Counties = ''
SELECT a.PROV_ID, a.PROV_NAME,
@Counties=coalesce(@Counties,'') + b.COUNTY + ','
from ECBH.dbo.tbl_PROVIDERS a inner join ECBH.dbo.tbl_Provider_Serv_Regions c
on a.PROV_ID = c.PROV_ID
inner join ECBH.dbo.tbl_Regions b
on b.REGION_ID = c.REGION_ID
where c.PROV_ID = a.PROV_ID
and a.MASTER = 1

I thought about creating a table to hold the coalesced values (need to coalesce two other fields as well), but wouldn't an insert to a table fail for the same reason?The counties table does not relate to the provider table, but does relate to a provider_county table (which in turn relates to the provider table).