In July 2020, a magnitude 7.8 earthquake struck off the coast of the Aleutian Islands, Alaska. It was the first of a sequence of large earthquakes in the region from 2020 to 2025 and broke a segment of the plate boundary that had been quiet for over 100 years. To understand what happened in the months leading up to this event, we analyzed thousands of small earthquakes that occurred in the area during the 10 months before the mainshock. Using advanced earthquake detection tools, we created a catalog of these small events—more than twice as many as previously recorded. We found that the seismicity rate began to increase about three weeks before the big earthquake, especially in a region offshore known as the 'outer rise.' We also observed that some of the earthquakes appeared to migrate closer to where the large earthquake would eventually happen. These patterns resemble results from previous studies on seismicity before other major earthquakes in Japan and Chile. Our findings suggest that small earthquakes, even in remote offshore areas, can provide important clues about how stress evolved and leads to large earthquakes. This work seeks to improve our understanding of precursory activity before large earthquakes.