Since we visited Grant's headquarters it only makes sense to visit Albert Sidney Johnston's as well. I've been there before. Its usually a spot I drive past the first time as the only sign for it is a low wooden marker directing you where to turn off highway 22. Now there is a larger Civil War Trails sign as well as more NPS signs that I remember.
This is the spot where Johnston camped the night before the battle and where he had a morning council with his generals to decide whether or not to engage the enemy. The early morning pickets brought on the engagement but Johnston used that as the sign to continue with their plans.
The site is not NPS property (at least as far as I know) and the homemade information papers inside the large sign at the site would indicate that it isn't NPS as well as one would expect them to have more permanent markers.
When I first started visiting this spot 10 or so years ago it felt out of the way and seldom visited, today it appears its becoming a more standard spot in the tour even if its not within the official park boundaries.