Tomlimson Simanjuntak, Nirm 0143130294, conducted a study of Factors Affecting the Development of farmergroups in District center of tapanuli the purpose of writing was. 1. Knowing and assessing the developmental level of the farmergroups, 2. Knowing the role of extension agent as motivator, innovator, informator and as a guide to the development of farmergroups. The study was conducted from April 3 to May 31, 2017 located in District Tapanuli center North Sumatra. the Method using survey techniques, sample of 91 people and using questionnaires was have been tested for validity and reliability. Data analysis using multiple linear regression analysis Y = 2.829 -0.015X1.1 -0.053X1.2 + 0.332X1.3 + 0.3037X1.4 + 0.359X2.1 + 0.004X2.2 The results of the assessment indicate a fairly high rate of group development. Factors that influence is the role of extension as an informatory, the role of counselor as a mentor and the role of local government in providing training, significant effect because the value of tcount> ttabel. While the role of extension as a motivator, innovator and the role of government in the form of fertilizer assistance does not affect the development of farmers in six sub-districts in District center of tapanuli