I checked the 1900 census of Lake County, IL and did not find your Paul Willson. Did he have any brothers or sisters? Sometimes the census records do not have the correct given names for children in families. The children may have been listed by a nickname or by a first name, when as adults they may have gone by a middle name, etc. You may want to check the soundex index for the state of IL in 1900 and find your Paul that way. Wilson is quite a common name, so you would have to go through quite a few families to check for a child with the name of Paul, but it may be the only way you will find the family. Good luck.