Complex sentence: The site where Plymouth Church is located was purchased from the First Presbyterian Church, which had been worshipping there since 1822, but which needed more space and moved to a new site on Henry Street, a few blocks away.
Split into simpler sentences: The site where Plymouth Church is located was purchased from the First Presbyterian Church, which had been worshipping there since 1822, but which needed more space. It moved to a new site on Henry Street, a few blocks away.