Arkansas has 75 counties, and ten of them are served by two county seats rather than one: Arkansas, Carroll, Clay, Craighead, Franklin, Logan, Mississippi, Prairie, Sebastian and Yell. Each is divided into two judicial districts, and each district keeps its own courthouse and its own records. The usual reason is terrain — a river or a ridge that once made a single seat unreachable for half the county's residents in bad weather — and the arrangement outlived the travel problem that caused it. Any table that stores one seat per county is therefore wrong for roughly one Arkansas county in seven, and wrong in a way that only shows up when somebody files in the district the table forgot.
The state's postal geography runs into the same ten counties. Arkansas has 706 codes under fourteen prefixes, and three of the six busiest are named for a city that shares its county with another seat: 724 around Jonesboro, which shares Craighead with Lake City; 723 around Blytheville, which shares Mississippi with Osceola; and 726 around Eureka Springs, which shares Carroll with Berryville. The sorting geography and the judicial geography were drawn for different reasons and neither defers to the other, so “the county's address” is an ambiguous phrase here in a way it is not in Kansas or Iowa.
The capital is the smallest surprise in the dataset. Prefix 722, whose principal place is Little Rock, carries 25 codes — fewer than any other prefix in the state, and less than a third of the 81 that 720 around Conway carries. Little Rock's own mail is split across neighbouring prefixes rather than concentrated under one, so a fixture that reaches for the capital to represent Arkansas picks the least representative prefix available. Drawing from 720, 721 and 724 instead exercises the sorting centres that actually move the state's volume.
One thing Arkansas does make easy: its fourteen prefixes run 716 through 729 with no gaps, so the whole state is a single unbroken block. That is worth knowing before you generalise, because a neighbouring state may not be built the same way — and a prefix rule written against a contiguous state and reused elsewhere fails quietly. Use the ZIP code generator if you need codes without the rest of an address.