The overall goal of rural revitalization is to realize agricultural and rural modernization. It is increasingly evident that without agricultural and rural informatization, such modernization cannot occur. As a result, the level of informatization development has become an important means of measuring the level of agricultural and rural modernization. Particularly as the application of modern information technology to agricultural and rural areas deepens and its achievements become increasingly evident, there is an urgent need to establish a scientific, comprehensive, and operable evaluation index to measure the level of development of agricultural and rural informatization. Based on six primary indicators—the development environment, basic support, production informatization, operation informatization, rural governance informatization, and service informatization—we establish an evaluation system for the level of agricultural and rural informatization development level. As well as the six primary indicators, the system includes 14 secondary indicators and 20 tertiary indicators, and is based on 2,642 counties in 31 provinces (autonomous regions and municipalities) in China. The relevant data of 2020 were collected to measure the overall level of county agricultural and rural informatization development in China and all provinces (autonomous regions and municipalities) in that year. The results of the empirical analysis show that the overall level of county agricultural and rural informatization development in 2020 is 37.9%, and that Zhejiang, Jiangsu and Shanghai ranked first, second and third in China respectively, in terms of the agricultural and rural informatization development level. We systematically summarize the phased important achievements in the development process of China’s agricultural and rural informatization from five aspects, including the rapid growth of e-commerce for agricultural products, and improvements in grass-roots governance digitization. In addition, we analyze the shortcomings in the process from four aspects, including but not limited to unbalanced and insufficient development and a low informatization level of agricultural production. This paper puts forward countermeasures and suggestions for promoting the high-quality development of agricultural and rural informatization and the overall revitalization of rural areas during the period of the 14th Five Year Plan.