Several parts combine into one character.

The traditional 縣 has one of the more grim etymologies in CJK: it is a compound ideograph showing 首 (head) inverted plus 系 (silk thread / connecting strand). The composite originally depicted an executed criminal's head suspended from a thread or cord — a public display of state authority. From this gruesome punishment-display image grew the abstract sense "the area subject to centralized authority" → administrative county / district. The character documents how political control over a region was conceived through the imagery of public capital punishment. Japan simplified to 県 (just 目 + 木-ish), Mainland China to 县.

Korean reading "hyeon." Korean uses 縣 only in classical/historical contexts: 縣監 (hyeon-gam, "county supervisor" — Joseon dynasty district magistrate, governing a 縣 of moderate size), 縣令 (hyeon-ryeong, "county order-issuer" — another Joseon-era local official rank). Modern Korean administrative geography uses (si, city), (do, province), (gun, county), (gu, ward) — 현 is essentially extinct in current Korean political vocabulary.

Mandarin xiàn, 4th tone (simplified 县). Modern Chinese keeps 县 actively as an administrative tier: 县 (xiàn, county), 县城 (xiànchéng, county seat — the principal town of a county), 县长 (xiànzhǎng, county head). The Chinese hierarchy is 省 (province) > 市 (city) > 县 (county) > 镇 / 乡 (town / village). Chinese 县 is comparable to American counties or French départements.

Japanese on-reading ケン (ken) — 県 (ken, prefecture), 県庁 (kenchō, prefectural government office), 県知事 (kenchiji, governor of a prefecture). 県 is the most common of Japan's four prefecture types: 都・道・府・県 (todōfuken). Japan has 47 prefectures total, distributed as 1 都 (Tokyo), 1 道 (Hokkaido), 2 府 (Kyoto, Osaka), and 43 県 (everywhere else from Aomori to Okinawa). When a Japanese person says 「私は東京から」 vs 「私は静岡県から」, the prefectural classification is implicit and significant.

Memory aid: a head suspended by a cord — public display of authority over a region became the administrative county.