Olathe is the county seat of Johnson County, Kansas, United States. It is the fourth most populated town in the metropolitan area of Kansas City and Kansas. The projected population is more than 135,000. Olathe is bordered to the north by the cities of Lenexa, to the east by Overland Park, to the north by De Soto and to the southwest by Gardner.The region has an approximate size of 60.42 square miles. Olathe worked on the Oregon Trail, the California Trail and the Santa Fe Trail as a stopover. Traveler catering became the primary source of revenue for local shops and enterprises. The trails to the west lost significance after the building of the transcontinental railroad and Olathe faded into obscurity and remained a small, sleepy prairie town.