I got that notice also and tossed it. Ours also is a hobby farm although we do have 75 chickens. I didn't even read what the questions were --- just figured it wasn't anybody's business. We never 'registered' our property anywhere but we are on the tax roles as unimproved acreage.

The USDA and state farm census statistics are actually important, even for a small operation. The results allow for estimating the national herd/flock numbers, and crop acreage, conservation acreage, et cetera, which in turn allows the farm programs to be managed with some sort of efficiency. It is used in many helpful ways with no negatives I am aware of. The census we do every 10 years is also required by law, has been for long, long time. I have done the farm census for over 25 years and never seen 1 negative from it.