Winchester is a city in Jefferson County, Kansas, United States. As of the 2020 census, the population of the city was 461. Winchester was laiā¦Winchester is a city in Jefferson County, Kansas, United States. As of the 2020 census, the population of the city was 461. Winchester was laid out in 1857. It was named after Winchester, Virginia. A post office in Winchester was established in March 1858 and closed in 2021.