COVID-19 led to a pandemic in 2020, which officially arrived in Colombia on 6 March 2020. As in other parts of the world, the spread of the virus was underestimated due to the lack of diagnostic tests and follow-up protocols. The present study estimates the number of daily cases of COVID-19 infection compatible with theoretical knowledge of the disease, seroprevalence studies, and records of daily deaths due to the disease. To this end, the REMEDID (Retrospective Methodology to Estimate Daily Infections from Deaths) algorithm was applied in nine Colombian cities. On average, official records detected only around 13% of the maximum number of infected persons in the first wave, which they dated with a delay of 25 days. In addition, there was an average delay of 30 days in detecting the first cases. In particular, in Bogotá, the city with the highest number of infections in Colombia, it was observed that (1) the first infected person arrived on 26 January 2020, 40 days before the official registration; (2) the maximum peak of infections was around 6 times higher than that recorded in the official statistics; and (3) this peak was reached on 08 July 2020, 39 days before the official registration date.