Wow, a question about Uruguay; these are pretty rare on AskHistorians! Anyway, emancipation was a convoluted process in Uruguay (and the Americas as I’m sure you know). /u/Ezterhazy gives a nice overview of the timeline and a useful primary source. I will echo his or her comment that abolition in Uruguay was not a sudden break with clear dates (though some important ones can be identified). Instead, the independence period gradually wore away the institution of slavery.

When we think about slavery, we tend to think only of places that received colossal numbers of African slaves like Brazil and the Caribbean; however, by the end of the colonial period, the Río de la Plata had one of the fastest growing slave populations. We don’t know for sure, but there were probably around 7,000 slaves in the Banda Oriental around the time of independence which was probably about a quarter of the Banda Oriental’s population. Most of these slaves were urban laborers like servants, cooks, and street vendors or engaged in rural occupations, especially agriculture and ranching.

Throughout the colonial period, there were a variety of ways for slaves to gain their freedom. The most common way was through manumission, where the slave bought his or her own freedom. This actually occurred fairly frequently in Spanish territories, with manumission rates in Buenos Aires sitting around 1.2 percent per year according to historian Lyman Johnson. Since the slave trade was a relatively recent development in the Banda Oriental, their manumission rate was around .9 percent according to George Reid Andrews in his book Blackness in a White Nation: A History of Afro-Uruguay. With the outbreak of the Wars of Independence, revolutionary leaders in the Río de la Plata began granting freedom to slaves who served in their armies for five years. Around 5,000 slaves joined Argentine revolutionary armies during the 1810s. Famously, half of San Martín’s army were soldiers of African descent. To further bolster their numbers, the revolutionary junta in Buenos Aires enacted Free Womb laws in 1813 to entice support from African populations.

Keep in mind, Uruguay did not yet exist; the territory was essentially a frontier area wedged between Buenos Aires, the Littoral provinces, the Guaraní provinces, and the southern Brazilian/Portuguese provinces. Spanish, Portuguese, Porteño, and eventually Liga Federal troops fought for control of the Banda Oriental, hammering out a new political order through a series of complicated conflicts and counter-conflicts that go beyond the scope of this reddit post. Of particular importance to answering your question, Artigas also promised freedom to slaves who joined his cause. Slaves from the Banda Oriental and even southern Brazil flocked to his movement, so much so that Brazilians complained about the damage the movement was causing to their livelihoods. Portuguese troops entered the Banda Oriental in 1811 and again in 1816. For the next seven years, conflict see-sawed between the forces of the Liga Federal, Buenos Aires, and Portugal (later Brazil once they became independent), culminating in the Cisplatine War and the creation of Uruguay.

Throughout these struggles, no one force held complete control over the territory, so laws were recognized by some but not by others. Slavery in the area continued, though the foundations of the institution were significantly weakened. During the conflict, slaves sought opportunities to fight when they were offered opportunities at freedom. Once the Banda Oriental declared independence from Brazil, the new government passed the Free Womb laws in 1825. Upon independence, the first constitution of 1830 recognized past freedoms, granted theoretical equality among all citizens, and abolished the slave trade, yet in practice, thousands of slaves were brought into Uruguay during the 1830s from Brazil.

It was the outbreak of yet another round of civil wars between the Colorados and the Blancos that led to complete abolition. In yet another effort to muster soldiers, the Colorados in 1842 abolished slavery and ordered conscription of all able bodied men into their forces. The Blancos followed suit in 1846, granting freedom to slaves in the territory without conscription. These laws remained in effect once the conflicted ended in 1851.

Like elsewhere in the Americas, emancipation did not bring equality; instead, it continued in a system of quasi-slavery called patronato. This was a practice started during the 1830s that basically extended a slave’s time in slavery by allowing his or her masters to prepare him or her for freedom. This practice was finally banned in 1853, marking the complete emancipation of slaves. However, Afro-Uruguayans would continue to face discrimination and low-pay, especially because their freedom coincided with the beginning of the massive European immigration wave that whitened the population and drastically reduce opportunities for blacks.

Hope this helps clarify where all those dates fall on the road to emancipation. In my view, abolition is easier to understand as a gradual process coinciding with independence that brought small victories over time.

Slavery was abolished in stages in Uruguay: firstly, after the declaration of independence from Spain, no-one born in the United Provinces of the Río de la Plata after 1814 was considered a slave; then, after Uruguayan independence in 1830, the importation of slaves was banned; and finally in December 1842, slavery was abolished in Uruguay.

As reported in the proceedings of an anti-slavery convention in London in 1843, here is the start of a decree issued by the Uruguayan senate on December 12 1842:

The Senate and Chamber of Representatives of the Oriental Republic of Uruguay, united in general assembly, considering:

That since the year 1814, those born in the territory of the republic should not be reputed slaves;

That since July of 1830, there should not have been any slaves brought into it;

It goes on to state that:

From and after the promulgation of the present resolution, there are no longer any slaves in the whole territory of the Republic.