The 1842 date is consistent with the first public documents associated with the house, mostly having to do with Crenshaw's trail in the kidnapping case of Maria Adams. However, records also exist that state that Crenshaw first hired a contractor to begin construction on the Hickory Hill house in 1833.
This is entirely consistent with the young Whig state representative Lincoln dropping by to call on a wealthy local resident while participating in debates in Shawneetown in 1840.
So what evidence do you have that Lincoln "new" about it? I'm not denying that the activities happened, after all Crenshaw was prosecuted for his criminal actions. But that's a long way from demonstrating that Lincoln was aware of his actions or approved of them.