Purpose: To determine the distribution of keratometry values in a wide age range of 6-90 years. Methods: In this cross-sectional study, samples were selected from two villages in Iran using multi-stage random cluster sampling. After completing optometry and ophthalmic examinations for all cases, corneal imaging was done using Pentacam, and keratometry values were determined. Results: Of the 3851 selected people, 3314 people participated in the study, and after applying the exclusion criteria, analyses were done on data from 2672 people. Mean age of the participants was 36.30 ± 18.51 years (from 6 to 90 years). Mean keratometry (mean-K) in flat and steep meridians was 42.98 (42.9-43.06) diopters (D) and 43.98 (43.91-44.07) D, respectively. Average of mean-K was 43.48 (43.41-43.56) D. Mean-K increased linearly up to the age of 70 years, and the cornea became slightly flat afterwards (coefficient = 0.01; P < 0.001). Mean-K was significantly higher in females (P < 0.001). Myopic cases had the highest mean-K (P < 0.001). The correlation of mean-K with age, gender, central corneal thickness, anterior chamber depth, pupil diameter, and spherical equivalent was investigated in a multiple regression model. Only older age and female gender showed a statistically significant association with mean-K. Overall, 31.62% (29.14-34.09) of the sample in this study had at least 1.0 D of corneal astigmatism. Conclusions: This is one of the few studies worldwide that demonstrates changes in keratometry in a wide age range from childhood to old age. Results indicated that age and gender are variables associated with keratometry.