Rocha who are reported to have a monthly wage bill of £6000 and some of whose players bicycle to training are the first team from outside Montevideo to win the title since the championship started in 1932.
The cow became famous when it was photographed on the field during a Rocha training session earlier in the competition.
Rocha opened up an unassailable four-point lead over Nacional with one match to play by beating nine-man Rampla Juniors 2-1 on Wednesday in front of a capacity 7000 crowd at their tiny stadium.
Forward Luis Magureguy scored both goals to put Rocha in the driving seat while the visitors had Martin Gonzalez and Carlos Aguiar sent off. Brazilian midfielder Nasa pulled one back for Rampla late in the game.
Jubilant fans ran on to the field at the end but still had to wait several minutes for the result of the Nacional's game with Miramar Misiones before the celebrations could begin.
That game ended 1-1. Sebastian Fernandez put Miramar ahead in the 15th minute before Gonzalo Castro equalised with six minutes to play.