Webb is a city in Clay County, Iowa, United States. The population was 138 in the 2020 census, a decline from 165 in 2000. The Webb post …Webb is a city in Clay County, Iowa, United States. The population was 138 in the 2020 census, a decline from 165 in 2000. The Webb post office opened in 1900. According to the United States Census Bureau, the city has a total area of 0.50 square miles, all land.