Mueang Nakhon Nayok (Thai: เมืองนครนายก, pronounced [mɯ̄a̯ŋ ná(ʔ).kʰɔ̄ːn nāː.jók]) is the capital district (amphoe mueang) of Nakhon Nayok province, central Thailand.

Mueang Nakhon Nayok is an ancient city. In the Ayutthaya kingdom it was the eastern frontier city. The historians^[who?] found the old city wall on three sides, the southern side was protected by the Nakhon Nayok River as a natural city wall.^{[citation needed]}

The district was called Wang Krachom as the office was in Tambon Wang Krachom, on the left bank of the Nakhon Nayok River. In 1896 the government moved the district office to the right bank of the river. The district office was moved to the old provincial court building in 1931. A new district office was opened on 18 January 1953.

The district name was changed to Mueang Nakhon Nayok on 1 January 1939, to correspond with the name of the province. On 1 January 1943, the government downgraded Nakhon Nayok Province and combined it with Prachinburi province, except Ban Na which became part of Saraburi province. During that time the district was called Nakhon Nayok District. On 9 May 1946, the government re-established Nakhon Nayok Province, thus the district was renamed Mueang Nakhon Nayok.

Neighboring districts are (from the southwest clockwise) Ongkharak, Ban Na of Nakhon Nayok Province, Kaeng Khoi, Muak Lek of Saraburi province, Pak Chong of Nakhon Ratchasima province, Pak Phli of Nakhon Nayok Province and Ban Sang of Prachinburi province.

The Sankamphaeng Range mountainous area is in the northern section of this district. The Nakhon Nayok River and Khlong Tha Dan are important water resources.

• Chulachomklao Royal Military Academy is in Phrommani Subdistrict, Mueang Nakhon Nayok District.

The district is divided into thirteen subdistricts (tambons), which are further subdivided into 125 villages mubans).^[1]

As of December 2023 there are: two municipalities (thesaban), of which Nakhon Nayok itself has town status (thesaban mueang) and covers subdistrict Nakhon Nayok and parts of Tha Chang, Ban Yai, Wang Krachom and Phrommani subdistricts. Tha Chang subdistrict municipality (thesaban tambon) covers part of the subdistrict. There are further twelve subdistrict administrative organizations - SAO (ongkan borihan suan tambon -o bo to)^[1][2]

Nakhon Nayok general hospital with 314 beds.
Chulachomklao Royal Military Academy Hospital with 90 beds.

There are total 17 health-promoting hospitals in the district, of which; one in Wang Krachom, Tha Sai, Don Yo, Si Nawa and Hin Tang and two in Si Chula, Dong Lakhon and Khao Phra and three in Sarika and Phrommani.^[3]

There are ninety-five Theravada Buddhist temples in the district.
One in Wang Krachom, two in Don Yo, four in Tha Sai, five in Nakhon Nayok and Tha Chang, six in Hin Tang and Si Chula, eight in Don Lakhon, nine in Ban Yai and Si Nawa, twelve in Khao Phra and Phrommani and sixteen in Sarika.^[4][5]