Kly is a municipality and village in Mělník District in the Central Bohemian Region of the Czech Republic. It has about 1,700 inhabitants.

Kly consists of seven municipal parts (in brackets population according to the 2021 census):

Kly is located about 4 kilometres (2 mi) south of Mělník and 20 km (12 mi) north of Prague. It lies in a flat landscape in the Central Elbe Table. The Elbe River flows along the western municipal border. Part of the Úpor – Černínovsko Nature Reserve is located in the municipal territory.

The first written mention of Kly is from 1323. The municipality was heavily damaged by the 2002 European floods.

Historical population

Year Pop. ±% 1869 894 —     1880 988 +10.5% 1890 1,015 +2.7% 1900 1,096 +8.0% 1910 1,238 +13.0%	Year Pop. ±% 1921 1,246 +0.6% 1930 1,313 +5.4% 1950 1,113 −15.2% 1961 1,064 −4.4% 1970 1,049 −1.4%	Year Pop. ±% 1980 990 −5.6% 1991 894 −9.7% 2001 921 +3.0% 2011 1,303 +41.5% 2021 1,629 +25.0%
Source: Censuses

The I/9 road (which connects the D8 motorway with Česká Lípa and the Czech-German border) passes through the municipality.

The main landmark is the Church of the Nativity of the Virgin Mary in Záboří. It is a Neo-Renaissance church from 1884, which replaced the old Gothic church.

In the centre of Kly is the Chapel of Saint Wenceslaus. It dates from 1886.

• Official website