Complex sentence: Offices were originally located in Hastings-on-Hudson, then moved to the Briarcliff College site in Briarcliff Manor; and are now located in Garrison, New York, on the former Woodlawn estate designed by Richard Upjohn.
Split into simpler sentences: Offices were originally located in Hastings-on-Hudson, and then subsequently moved to the Briarcliff College site in Briarcliff Manor. Hastings is now located in Garrison, New York, on the former Woodlawn estate designed by Richard Upjohn.