It depends on the style guide that you're following; there are many. CMS/ Chicago Manual of Style is one; AP or Associated Press is another. Here's an example from the AP:
dates, months, years, days of the week
For dates and years, use figures. Do not use st, nd, rd, or th with dates. Always capitalize months. Spell out the month unless it is used with a date. When used with a date, abbreviate only the following months: Jan., Feb., Aug., Sept., Oct., Nov. and Dec.