The area code for the northeastern region of Florida, including Jacksonville, is 904. 904 is the area code representing northeastern Florida, covering the entire city of Jacksonville, Duval County, and nearby St. Johns County (including St. Augustine), Nassau County, Clay County, Baker County, and Putnam County. All these areas are part of the Jacksonville Metropolitan Area.

The history of the 904 area code dates back to 1947 when all of Florida used a single area code, 305. Due to population growth and a surge in phone demand, area codes were split, leading to the creation of 904 in 1965. At that time, it covered a wide area that included northern and parts of central Florida. Later, as central and southern Florida were divided into 407, 305, and 321, 904 remained solely for northeastern Florida. To this day, although the population in the Jacksonville area has increased, it continues to operate under the single 904 area code, and while there have been concerns about number exhaustion, no additional area codes have been introduced yet.

For those new to the U.S. phone numbering system, a U.S. phone number consists of 10 digits (in the NXX-NXX-XXXX format). The first three digits are the area code, the next three are the exchange/prefix, and the last four are the subscriber number. For example, if the Jacksonville City Hall number is 904-XXX-XXXX, then 904 is the area code. When calling Jacksonville from another area in the U.S., you would dial 1-904-XXX-XXXX, adding the country code 1 in front. Within the same 904 area, there were instances where only the 7-digit number (XXX-XXXX) could be dialed, but currently, most carriers require the full 10-digit input.

Emergency calls can be made to 911 nationwide. For non-emergency police reports, you can contact the Jacksonville Sheriff's Office (JSO) non-emergency number. 211 is for social service information, and 311 is the city government service and information number. In Jacksonville, you can use 311 to report issues related to COJ (City of Jacksonville), such as garbage collection, road damage, and park problems. 811 is the number to confirm the location of underground utilities, which must be reported before digging. For international calls to Korea, the format from the U.S. is 011-82-XX-XXXX-XXXX, while smartphones use the format +82-10-XXXX-XXXX.

When starting life in Jacksonville, it's helpful to save a few useful numbers in advance. JEA (Jacksonville Electric Authority): 904-665-6000, JTA (Jacksonville Transportation Authority): 904-630-3100, Duval County Tax Collector: 904-255-5700, COJ Services: 904-630-CITY (2489) are some of them. These numbers will be needed for utility connections, garbage collection requests, and address changes right after moving in.