23 February 1854
The Republic of the Orange Free State was established by the signing of the Bloemfontein Convention (also called the Orange River Convention) between Sir George Clerk (for Britain) and twenty-five 'representatives of the people' in Green Lodge, Bloemfontein. The convention guaranteed the independence of the territory between the Orange and Vaal Rivers. In addition to the declaration of independence, the document also contained clauses regarding treaties with indigenous people, prohibition of slavery, and regulating trade.
References

Potgieter, D.J. et al. (eds) (1970). Standard Encyclopaedia of Southern Africa, Cape Town: NASOU, v. 2, p. 373.| Wallis, F. (2000). Nuusdagboek: feite en fratse oor 1000 jaar, Kaapstad: Human & Rousseau.