Yeah, I learned about that one just last night at Rick Kerrigan's Humbolt Bay Mycology Society talk, so I'm thinking it probably is not very common here since it hasn't turned up elsewhere yet.

Here is some text to copy and paste for this species, could probably use the same text for all of North America: "Agaricus campestris has only been found twice in North America from all of the sequencing that has been done here by Rick Kerrigan, Stephen Russell, and others. It is therefore doubted that is the most common Agaricus here. In fact, it may even be pretty rare. Looking at the preponderance of observations of this name here at the start of 2021 one might think it is the only common Agaricus mushroom, here in the eastern U. S. anyway. It is extremely similar looking to other Agaricus mushrooms and requires a trained eye to tell apart. Unfortunately, it seems at the moment, the only way to reliably confirm it is through a sequence or possibly with a microscope. Mushrooms that look like this are often some really good edibles in sections Agaricus, Subrutilescentes, and Arvenses. We are interested in diminishing the error created by the computer vision with Fungi. If you would like to help or are curious about it, please read what is written here https://tinyurl.com/y9qqjf3z and get started. Here is a picture of the second N. A. sequenced specimen of Agaricus campestris, from Michigan, https://mushroomobserver.org/389487 to compare yours to."