The Constitution of Jammu and Kashmir came into force on :

The Constitution of Jammu and Kashmir was adopted and enacted by its Constituent Assembly on 17 November 1956 . While certain preliminary sections came into force immediately upon adoption, the remaining provisions and the formal commencement of the Constitution occurred on 26 January 1957 . This date was specifically chosen to coincide with the anniversary of the commencement of the Constitution of India . Until its abrogation in 2019, this document defined the state's relationship with the Union of India, declaring Jammu and Kashmir an integral part of the Union [4]. The state's territory was defined as comprising all areas under the sovereignty of the Ruler as of 15 August 1947 [4]. The special status and the separate constitution were eventually superseded by the Presidential Order of 2019 and the Jammu and Kashmir Reorganisation Act [2].

Sources

1. [4] Indian Polity, M. Laxmikanth(7th ed.) > Chapter 4: Salient Features of the Constitution > III Lengthiest Written Constitution > p. 28
2. [1] https://aasc.assam.gov.in/sites/default/files/swf_utility_folder/departments/aasc_webcomindia_org_oid_4/menu/document/the_constitution_of_jammu_and_kashmir_1956_1.pdf
3. [2] Introduction to the Constitution of India, D. D. Basu (26th ed.). > Chapter 15: Jammu and Kashmir > CHAP. 151 > p. 303