Per data sensus Jepang, <ref>[{{Cite web |url=https://www.citypopulation.de/php/japan-kanagawa.php |title=statistik populasi Hayama] |access-date=2023-04-29 |archive-date=2020-10-22 |archive-url=https://web.archive.org/web/20201022114926/http://citypopulation.de/php/japan-kanagawa.php |dead-url=no }}</ref> populasi Hayama telah tumbuh relatif stabil sampai sekitar tahun 2000 dan sekarang sedikit menurun.
* {{flagicon|Jepang}} – [[Kusatsu, Gunma]], sejak Maret 1969
* {{flagicon|Australia}} – [[City of Holdfast Bay]], [[Australia Selatan]] (Australia) sejak 1997;<ref>{{cite web|title=Kota Holdfast Bay|url=http://www.holdfast.sa. gov.au/site/page.cfm?u=937|archive-url=https://web.archive.org/web/20100531052749/http://www .holdfast.sa.gov.au/site/page.cfm?u=937|archive-date=May 31, 2010-05-31|url-status=dead|access-date=2023-04-29|dead-url=no}}</ref> 18 November 2009, Holdfast Bay menulis surat yang ditandatangani oleh Wakil Walikota menegur Hayama untuk perburuan paus Jepang di Samudra Selatan.<ref>{{cite news|date=18 November 2009|title=Holdfast Bay ingin menyelamatkan paus|url=http://guardian-messenger.whereilive.com.au/news/story/holdfast-bay-bid-to-save-the-whales/|publisher=[[Guardian Messenger]]|access-date=18 November 2009|archive-date=2012-03-01|archive-url=https://web.archive.org/web/20120301071621/http://guardian-messenger.whereilive.com.au/news/story/holdfast-bay-bid-to-save-the-whales/|dead-url=no}}</ref>
