3 sentences

1. 一月通常是最冷的月份。

   Yī​yuè tōng​cháng shì zuì lěng de yuè​fèn.

   January is usually the coldest month.

   Source: Tatoeba

2. 一月是一年的第一个月。

   Yī​yuè shì yì​nián de dì​yī gè yuè.

   January is the first month of the year.

   Source: Dong Chinese Dictionary

3. 农历一月也叫正月。

   nóng​lì Yī​yuè yě jiào Zhēng​yuè.

   The first month of the lunar calendar is also called Zheng Yue.

   Source: Dong Chinese Dictionary