When researching U.S. federal statutes or U.S. state statutes, you can usually find the full-text online.
For in-depth research, consult the annotated code versions via Lexis (U.S. Code Service and selected state annotated codes) or Westlaw (U.S. Code Annotated and selected state annotated codes).
Municipal (city) codes are often available online -- ask a reference librarian for assistance.