Gridley is a city in Coffey County, Kansas, United States. As of the 2020 census, the population of the city was 313. Gridley was founded in ab…Gridley is a city in Coffey County, Kansas, United States. As of the 2020 census, the population of the city was 313. Gridley was founded in about 1886. The first post office in Gridley was established on June 23, 1886.