Here is the full list. I probably did not notice Boston in the list before.

https://www.united.com/web/en-US/con...s/default.aspx

United hubs and key airports:

Boston, MA — Boston Logan International Airport (BOS)
Chicago, IL — O'Hare International Airport (ORD)
Cleveland, OH — Cleveland Hopkins International Airport (CLE)
Denver, CO — Denver International Airport (DEN)
Frankfurt, Germany — Frankfurt International Airport (FRA)
Guam — Antonio B. Won Pat International Airport (GUM) (also known as Guam International Airport)
Houston, TX — Houston/ George Bush Intercontinental Airport (IAH)
London, United Kingdom — London Heathrow International Airport (LHR)
Los Angeles, CA — Los Angeles International Airport (LAX)
Newark, NJ — New York/ Newark Liberty International Airport (EWR) [our New York area hub]
San Francisco, CA — San Francisco International Airport (SFO)
Tokyo, Japan - Tokyo Narita Airport (NRT)
Washington, D.C. — Washington Dulles International Airport (IAD)