Hnojník (Polish: Gnojnikⓘ, German: Hnoynik, Gnoynik) is a municipality and village in Frýdek-Místek District in the Moravian-Silesian Region of the Czech Republic.

The first written mention of Hnojník is in a Latin document of Diocese of Wrocław called Liber fundationis episcopatus Vratislaviensis from around 1305 as Gnoynik.

Politically Hnojník belonged initially to the Duchy of Teschen, from 1327 a fee of the Kingdom of Bohemia.

After the 1540s, Protestant Reformation prevailed in the Duchy of Teschen and a local Catholic church was taken over by Lutherans.

It was taken from them (as one from around fifty buildings) in the region by a special commission and given back to the Roman Catholic Church on 23 March 1654.

According to the censuses conducted in 1880–1910 the population of the municipality dropped from 599 in 1880 to 569 in 1910 with a dwindling majority being native Polish-speakers (from 97% in 1880 to 90.5% in 1910) accompanied by a German-speaking people (between 3% and 3.5%) and Czech-speaking (growing from 8 or 1.4% in 1890 to 34 or 6% in 1910).

Following the Munich Agreement, in October 1938 together with the Trans-Olza region it was annexed by Poland, administratively adjoined to Cieszyn County of Silesian Voivodeship.

The Baroque castle was rebuilt in the Empire style in the first half of the 19th century according to the plans of the architect Joseph Kornhäusel.