The word us should always be capitalized in titles. Admittedly, it is a very short word, and many other equally short words, such as to, the, by, or, in, and an, are not capitalized in titles. But that doesn’t mean that all short words should be lowercased. This only applies to certain word classes, namely, prepositions, articles, and conjunctions. Us, however, is a pronoun and therefore must be capitalized in title case, as in these examples:
’Til Death Do Us Part
Nothing’s Gonna Stop Us Now
A Place for Us to Dream
Take a look at the Title Case Converter, which not only capitalizes your titles correctly, but also tells you why each word is capitalized or not.