How can I find a death notice regarding Robert Hendricks, who died in
Illinois (probably St. Clair County), between 1990 and 2004.  I'm
really looking for his sister Barbara's married name and any
information I can find about her.  We want to find her for a reunion.

Try the website for the St. Clair County Clerk's Office:
http://www.stclaircountyclerk.com/vitalrecords.asp

Or try http://www.vitalrec.com/il.html#State to access the State of
Illinois' vital records.

I searched on belleville.com (in the Belleville News Democrat, a St.
Clair County newspaper), but came up with nothing, likely due to the
fact that the information you are requesting is too old & not in their
archives.  Unless, of course, you have the incorrect area.

I found the following listing on
http://www.iltrails.org/ford/obits8.html, which has Ford County,
Illinois death records (another source said it was Champaign County): 
ROBERT HENDRICKS Gibson City - Robert Hendricks, 68, of Gibson City
died Monday 10-2-2000 at his son's home in Bloomington, Minn.

You could also try accessing the Social Security Death Index: 
http://ssdi.genealogy.rootsweb.com/

It would be helpful if you had his approximate date of birth (at least
the year), city where he lived, occupation, wife's name, etc.

Sorry I couldn't help more; good luck to you.

~betsy63

Do you have any more information about this man--his estimated age or
date of birth, his wife's name, his occupation, children's names,
exactly what city in Illinois he was from or known to have lived in?

GENEALOGICAL RESEARCHER

You could try searching through the Social Security Death Index
http://www.obitcentral.com/obitsearch/ssdi.htm first to see what his
death date is (if he died with benefits).   Then you could try using
several of the obit resources on the web such as Obitsarchive:

http://oa.newsbank.com/enter/obcent?d_place=United%20States

There are many genealogy tools out there that can provide a lot of
information in a very short amount of time.   I recommend
GenealogyBuff.com http://www.genealogybuff.com because upon submitting
a surname, you can access many of the "hidden" internet databases that
exist to see what returns you get.  There will be obituary archives,
free vital records databases, paid databases, birth records, death
records, county records, census records, etc.
There is also a library of files that have early and recent data
arranged by state and county.
Hope this helps in your effort.