Objective: To describe the distribution and associations of demographic, familial, medical, and ocular factors with intraocular pressure (IOP). Methods: A cluster stratified random sample of urban and rural residents of Victoria, Australia, aged 40 years and older. Participants completed an interview and underwent a standardized dilated ophthalmic examination including measurement of IOP with an electronic applanation tonometer (Tono-Pen). Glaucoma status (possible, probable, definite) was determined by a consensus panel. The main outcome measure was IOP. Results: The mean age of the 4576 participants was 59 years, 53% were women, 32% were born overseas, and 132 had open-angle glaucoma. Geometric mean (SD) IOP was 14.3 (±1.5) mm Hg. The relationship between IOP and nuclear sclerosis, iris color, and family history of glaucoma depended on glaucoma status. In those with glaucoma, family history of glaucoma and country of birth were significantly associated with IOP in multivariate models (model: r2 = 0.08, P = .01). In the group without glaucoma, place of residence, use of alcohol, iris color, vitamin E intake, and spherical equivalent were associated with IOP (model: r2 = 0.01, P = .006). Conclusion: In participants with glaucoma, genetic factors seem to be stronger predictors of IOP, whereas in those without glaucoma, lifestyle and physiological factors seem to play a greater role.