Greetings Jeff:
Black walnut, for optimum growth and development, requires moist, deep fertile soils with a pH ranging from 6.5 - 7.5. Granted, walnut can grow on soils across a wide range of pH (4.5-8.5); however, that does not mean your planting “site” is an optimum black walnut location as there are other site factors that come into play (soil fertility, internal soil drainage, soil moisture, etc.). Even after you’ve found an optimum site or at least a good site, you will need to properly plan for the logistical aspects of managing a walnut plantation (site preparation; cover crops; seedling stock selection; annual maintenance such as herbicide applications to control perennial grasses; future pruning and selective crown thinning; etc.).
If you are going to plant one acre of black walnut as a future investment, I would probably plant at least 436 trees per acre: plant one tree every ten feet within your tree rows, with ten feet between tree rows (i.e., 43,560 square feet per acre divided by 10x10 spacing yields 436 trees per acre). 8x10 spacing (i.e., plant one tree every eight feet within the tree rows, with ten feet between tree rows = 545 trees per acre) is how I would design my tree planting if I were in your position and if I were using standard bare root seedlings.
On excellent sites, it may be possible to grow veneer-quality trees within a 40-year time horizon. On good quality sites, you're probably looking at 40-60 years. Seeing that you live in Savoy, might I suggest you swing by my office on campus and we can discuss your objectives and options to determine whether or not black walnut is the ideal species to plant on the site you have in mind!
Walnut Timber Prices:
http://web.extension.illinois.edu/forestry/il_timber_prices/pdf/itp_aug2009.pdf
http://web.extension.illinois.edu/forestry/blogs/eb94/
