Neighbouring municipalities are Kannonkoski, Konnevesi, Laukaa, Saarijärvi, Uurainen, Vesanto and Viitasaari.

Folk etymology connects the name to the word ääni "sound", but Terho Itkonen has suggested another origin: a Sámi term meaning "big, large" (compare Northern Sámi eanas, "most").

Four municipalities have been consolidated with Äänekoski: Äänekosken maalaiskunta in 1969, Konginkangas in 1993 and Sumiainen and Suolahti in 2007.

Äänekoski is located along Finnish national road 4 approximately 40 km north of Jyväskylä.

Finnish national road 69 to Suonenjoki begins in Hirvaskangas, 12 km south of Äänekoski center.

Finnish national road 13 between Kokkola and Lappeenranta passes through Honkola, 6 km south of Äänekoski center.

Modern Äänekoski is a product of a merger of multiple former municipalities, where the following villages were officially named: Besides these official divisions, the following villages or neighborhoods are also informally recognized: Hietama, Hirvaskangas, Laajaranta, Liimattala, Mämme, Parantala ja Rannankylä.

It is also defined by the fractured Lake Keitele, which stretches generally in the southwest-northeast direction from Äänekoski center to the open waters of Keitele proper in Havusalmi, but which has multiple bays in the perpendicular, southeast-northwest direction.

There are three urban areas: Äänekoski center (12,899 inhabitants), Konginkangas (445) and Sumiaisten kirkonkylä (church village of Sumiainen, 406).