American Kestrels (Falco sparverius) are declining across much of North America, yet the initial timing of the population decrease is unclear. In an attempt to elucidate when kestrel declines began, we examined historical descriptions of abundance within the northeastern United States. Within The Peregrine Fund's research library, we found 54 descriptions of kestrel abundance in northeastern states dating from 1839 to 2013. Our analysis indicates a cubic trend in descriptions of kestrel abundance with a peak occurring in 1951. After that peak, the population began its current decline, yet the population appears to have been stable beforehand. That the current decline is apparent in our data set lends credence to our methodology and suggests that populations were likely secure until approximately 1951. Our results thus suggest that populations of American Kestrels in the northeastern United States began declining before systematic monitoring began in 1966. Future research should thus examine what environmental changes occurred around the early- to mid-20th century in the northeastern USA to cause population declines of American Kestrels.