California frequently numbers uses decimal points in numbering its statutes. For instance, California's criminal trespass law is an unwieldy behemoth, commencing at Penal Code section 602. Section 602's intricate, specific, and often inapplicable definitions of trespass consists of subsections and subdivisions of those subsections, going so far as 602(y), which prohibits the avoidance of security screening procedures in courthouses and other public buildings. Beyond section 602, a number of other decimal-pointed 602 sections further define instances of trespass, including the amazing section 602.12 which prohibits entry onto land with the purpose of interfering with research. To see section 602 and the following sections, you can find a list of those statutes here.
But despite California's frequent use of decimal points, there are several examples of fractional statutes and sections. A quick search of Westlaw reveals that California has repealed or renumbered numerous sections that contained fractions rather than decimal points. But several fractional statutes still exist. These mainly appear in California's Water Code Appendix, which contains several fractional sections, including section 28-141 1/2 which specifies the code sections governing claims for money damages against water districts. There is also section 33-281 1/4(o) which deals with the lease and sale of land deeded to water districts as a result of tax delinquency.
California's constitution also contains at least one example of a fractional section. Article 9, Section 6 1/2 states that the California Constitution does not prohibit the formation of school districts in multiple counties or the issuance of bonds by those districts.
I have not looked into the codes of other states to see if the practice of fractional sections is more widespread. But from my cursory investigation into California law, it looks like these sections are holdovers from historic practices of numbering statutes with fractions rather than decimal points.
I think that the use of letters or decimal points rather than fractions is a better way of organizing statutes. And I am not aware of citation rules for citing fractions. For instance, does there need to be a space between the section number and the fraction? Does the fraction need to be formatted as 1/2 or ½? I am not aware of the answers to these questions. Ultimately, decimal points and letters are easier to work with, and California's fractional statutes remain as a quirky remnant of old drafting practices.