Cachoeira do Sul () is a municipality in the state of Rio Grande do Sul, southernmost Brazil.
Its Marian Catedral da Nossa Senhora da Conceição is the episcopal see of the Roman Catholic Diocese of Cachoeira do Sul.
It is located at a latitude of 30ú02'21" S and a longitude of 52ú53'38" W, at an approximate elevation of 68 meters above sea level. Its population in 2020 was approximately 81,869 and its area is 3715.5 square kilometers.
Cachoeira do Sul has a humid subtropical climate and its annual average temperature is . In January, the warmest month, highs frequently surpass with the average low dropping to . In June, the coldest month, highs reach and lows usually go below , reaching up to , but snow is a rare occurrence. Rainfall is distributed evenly throughout the year with a monthly average of .
There are two soccer teams in Cachoeira do Sul, Grêmio Esportivo São José and Cachoeira Futebol Clube they both play at the Joaquim Vidal Stadium.