In Websters 3rd New International (unabridged) it is raccoon with two c's. [Come visit the big dictionary in the library.] That is also the preferred spelling in The New York Times, The Compact Oxford English Dictionary and The American Heritage© Dictionary of the English Language 4th Ed.
Raccoon is also the spelling used by the County (all documents), the State (by a score of 218 to 2) and among the documents collected by CDC (374 to 37)
Spelling checkers vary. Some accept only the 2-c version, others will also accept the 1-c variant "racoon". In Takoma Park people have been spelling it both ways, sometimes within the same paragraph. Does it matter? Yes, it does. If you are searching for information, spelling matters.
In reference we now have the complete OED, with all supplements, on CD-ROM. You no longer have to use a magnifying glass! We also have a new dictionary - R 423.1 Oxford reverse dictionary for those times when you know the meaning but can't remember the word.
BTW - Do you know about Honcodes? Medical information on the web is notoriously untrustworthy and can be very dangerous. At least try to be certain that any site from which you obtain medical information has HONcode certification (as determined by the Health on the Net foundation). Such certification tells you that the producers subscribe to a certain set of professional ethics which includes revealing the sources of the information. To assess value you will need to also look closely at the credentials of these sources. The rule is - Are the sources of the information cited and are those sources credible? HONcodes help with the first part of the rule, you have to bring your own judgement to the second.
How do you know if a site has HONcode certification? You can look for the certification logo on the main page at the site. For example, go to Intellihealth (Aetna and Harvard Medical School) and look down at the bottom of the page.
If you use Firefox as your browser (as we do in the library) you can make it even easier by putting a HONcode tester on your tool bar. If you frequently look for medical information, go get the extension.