Usage-based constructionist approaches see language as an inventory of constructions at different levels of schematicity learned from the input. If so, personal constructicons should vary as a function of usage. Repeated use and chunking/entrenchment of concrete instances should lead to reanalysis of their internal structure and change in the level of schematicity. This paper exploits the reduction probability of is in it is as a diagnostic of reanalysis in a 1.75-million-word diachronic corpus of a single blogger over 8 years. All instances of it is/it’s (n = 10,929) were annotated at the constructional and lexical levels. A multilevel logistic regression model showed significant fixed effects of constructional entropy and construction-to-word association on reduction probability. Importantly, there remained substantial variation across lexical types of constructions in the extent to which they associated or became associated with reduction over time, suggesting idiosyncratic entrenchment and potential reanalysis as a function of usage.