For the most part, U.S. Citizenship and Immigration Services (USCIS) reviews applications on a first-come, first-served basis. (Everyone, however, must stand in line behind the employment-related petitioners who have paid extra for “premium processing.”).
Also, in certain family visa cases, USCIS may take longer to make decisions on I-130 petitions where the beneficiaries' priority date will not be current for many years, such as in the case of the brother or sister of a U.S. citizen. This does not hurt the person's case, because their place in line for a visa has already been established by their “priority date,” which is the date that USCIS first received the form I-130 petition.
processing times vary depending on the service center that is processing your application or petition. Each service center has been specifically designated to handle specific types of immigration benefits. The type of center that will process your case depends on a number of different factors including: the type of immigration benefit you are requesting, your immigration category, and also your state of residency.
Since some types of immigration benefits are in great demand, such as permanent residency, service centers handling these types of applications generally have a heavier workload than others. Unfortunately, this means that processing times for service centers with heavier workloads will be longer than others. USCIS has tried to balance the workload by transferring some petitions to other service centers that do not have such a heavy workload. These efforts have been made to try to speed up the adjudication process.
Second, processing times also vary depending on whether an interview is required for the benefit you are seeking. If your petition requires an interview, the time it will take for you to receive an interview notice will depend on the waiting period of your local field office, the volume of applications received at that office, your place in line for an interview, and of course the current office closures.