what is the zip code for o'fallon missouri
63366 Zip Code Profile. 63366 is a rural zip code in O Fallon, Missouri. The population is primarily white, and mostly married couples. At $188,300 the average home value here is a bit higher than average for the St. Louis metro area, so this probably isn't the place to look for housing bargains. The average family income here is $66,959/year.