Over the past three years, nature-based preschools, forest kindergartens, and outdoor preschools (collectively, nature preschools) in the US have more than doubled to 585, and nature preschools can now be found in nearly every state in the United States. Over the past decade, this represents a nearly 25-fold increase. As nature-based education is becoming an increasingly popular choice in preschool education, nature preschools are emerging as a specialized preschool option not unlike other approaches to early childhood education, such as Montessori or Reggio-Emilia schools. In addition, the 585 programs reported here represent only schools that have fully adopted nature-based education as the core of their program; countless other schools are incorporating nature with gardens, outdoor classrooms, field trips, partnerships with environmental education centers, and in many other ways. (author abstract)