The objective of this study was to evaluate the impact of a trap-neuter-return (TNR) event on the size of free-roaming rural cat colonies in Quebec. This prospective randomized, controlled study included 18 cat colonies around barns and stables that were randomly assigned to either a TNR group (10 colonies of 7 to 27 cats; 14.3 cats on average) or a control group (8 colonies of 7 to 26 cats; 14.5 cats on average). The number of cats in each colony was calculated from the images obtained by camera-trapping at: baseline (T0), 7.5 mo (T7), and 12 mo (T12). At baseline, the TNR group was subjected to a TNR event. When taking into account adults only, a significant growth difference was observed in the number of cats between the TNR group and the control group at T7 (P = 0.03). When including kittens as well as adults, a trend towards a lower growth of the TNR group compared to the control group was noted at T7 (P = 0.06). There was no difference in the number of kittens between the 2 groups at T7 (P = 0.49) or at T12 (P = 0.36). There was a trend towards more emigration in the control group at T12 (P = 0.095). Isolated TNR events have a low and temporary impact on colony size in Quebec's rural cat colonies.