This is the 4623rd most frequent Japanese word.
所沢
Tokorozawa: A city located in Saitama Prefecture, Japan.
The usage of 所沢 here is as a proper noun, referring to the city/town in question.
所沢は埼玉県にあります。
Tokorozawa is located in Saitama Prefecture.
In this context, 所沢 emphasizes the location where the park is situated.
所沢にある公園はとても美しいです。
The park in Tokorozawa is very beautiful.
Here, 所沢 acts as the starting point of the journey mentioned.