Most schools in the United States have websites, but there is no publicly available information to suggest that all schools in the country have websites, as of 2015. Department of Education websites of respective states and K12Education.com are resources that provide lists of schools in all states in the country.
K12Education.com lists schools in all the 50 states in the United States. It also has individual pages dedicated to schools and publishes useful information such as school size, demographics, ethnicity and subgroups. High-Schools.com, NewsWeek.com and NeighborhoodScout.com have published numerous lists of top schools in the country with a direct link to school websites where available.