We employ a network‐based method to map the spatiotemporal variations of the magnitude of completeness (Mc) in the Composite Alberta Seismicity Catalog (CASC; see Data and Resources) from 1985 to 2015 across a grid of sites. The underlying principle is that we expect events to be located and cataloged if they are detected on four or more seismic stations. Seven Mc maps are created to represent spatial variations of Mc in time periods: 1985–1989, 1990–1999, 2000–2006, 2007–2009, 2010, 2011–2013, and 2014–2015. By counting the annual number of events above Mc since 1985, and assuming a Gutenberg–Richter b‐value of 1.0, we calculate the equivalent number of M≥3 earthquakes in eight relatively active grid cells. In several areas, there is clear evidence of changes of seismic rate over time. Overall, seismicity in Alberta is highly clustered in both space and time.