Census' gathering was generally based on townships. The term was used to define an area and was part of the scheme to map the country.The names ofthe townships often has nothing to do with communities such as cities/towns/villages that were within their boundaries.
My sources do not reflect a O'Neill community in San Joaquin Co.An Expedia map search using O'Neill in CA also does not reflect any geographic locations in San Joaquin county.
However, one of the townships listed in the 1930 census is the O'Neal Township (spelling difference).It apparently overlapped at least some of the boundaries of the city of Stockton CA.
One potential source of additional info is the City Directories at the main library in Stockton.I have used them in the past to obtain expanded info on individuals such as addresses, trade, employer, relatives living with, etc.I'm not local and can't help you with research.Am not sure whether this data is available on-line, but suspect if it is, it's not free.Possibly someone who is local would be willing to do some look-ups.If you make a request, you should provide as much in the way of specifics that you have, since the surname is not that uncommon.