The following url tells how to research in Swedish parish records.http://genforum.genealogy.com/johnson/messages/31874.html
I checked the handwritten parish records on the fee-based Genline site and didn't find his birth in Västervik parish on the date you provided. Perhaps the date is incorrect or perhaps he was born "near" Västervik but not "in" Västervik or there is a different/smaller Västervik. Perhaps someone has the time to dig through the SCB records (extractions of birth, marriage, and death records sent each year to those in Stockholm dealing with statistics. Those are arranged by county and are on Genline.) to find the parish where he was born.http://www.genline.com
In modern times Västervik is a kommun (municipality/township) with a lot of parishes. The kommun didn't exist back then but this may give you an idea of other parishes to check for his birth record.http://www.skatteverket.se/folkbokforing/sverigesforsamlinga...
Ed, se Västra Ed
Gamla Västervik, se Gamleby
Hallingebergs norra kbfd*
Hallingebergs södra kbfd*
Nya Västervik, se Västervik
Unfortunately I don't see him with that birthdate and birthplace (or even the birth county) on the Emibas CD. Emibas was made from registrations in the Swedish parish to go to a foreign country. It is about 75% complete. His name is far too common to identify him leaving from Västervik parish on the Emihamn database, made from registrations with Swedish port police before leaving Sweden. (Not all Swedes left through a Swedish port.) The problem is made worse by not knowing what form of "Johnson" he used. It was probably Johansson, Johannesson, Jonsson, Jönsson, etc.
You can find a year of immigration in the U.S. Federal Censuses for 1900-1910-1920-1930. Also compare the information about month and year of birth found on the 1900 U.S. Federal Census to the date you provided in your message.