The library is located in the park.

is 是 be 动词的第三人称单数现在式，表示"存在"或"处于某种状态"。 located 是动词 locate 的过去分词形式，表示"位于、坐落于"。 in 是介词，表示"在...里面"或"在...范围内"。 is located in 是一个固定搭配，表示"位于...内部"或"坐落于...之中"。