Most online versions of various codes are updated within 48 hours of legislative changes. Check the currency note at the beginning of the code or code section when looking online - such as in Lexis, Westlaw, Bloomberg Law, FDsys or at a state's legislative website.
The U.S. Code Classification Tables are useful for identifying very recent additions and amendments to the U.S. Code. These tables are sorted in U.S. Code order as well as by public law number.
For recently enacted federal legislation in slip law or otherwise, visit Congress.gov. This website can be word/phrase (or index) searched by date for proposed additions or amendments to the U.S. Code. Congressional bills are also word/phrase searchable at FDsys.
State legislative sites offer bills in full text and commonly provide keyword searching and bill status information. In addition, commercial databases such as Westlaw and Lexis provide state session law searching for state code updates.
Check the pocket part in the back of the volume or the cumulative supplement. These supplements are usually published annually. Look for legislative service pamphlets. These updates are published throughout the year and usually include a cumulative list of statutes affected by recently enacted laws and a cumulative subject index.
Tables of amendments and repeals published in codes and advance legislative services provide citations to session laws that modify existing statutes. All three versions of the U.S. Code and Statutes at Large through 1976 contain tables of amendments, repeals and new code provisions.
To establish the current validity of an existing statute, find and read case law (in your jurisdiction) that cites your statute. Look out for court constitutionality rulings and other holdings affecting the statute's "good law" status.
If you are looking at a statute in a commercial database like Lexis, Westlaw or Bloomberg Law, then you can use a citator (like Shepard's or Key Cite) to locate current materials that analyze your statute, such as cases and secondary sources.