This study evaluates the internal control and the severity indices of control factors in the building industry in Ondo State, Nigeria. A survey research design was used for this study. A well-structured questionnaire was designed to collect data for the study. A non-probability sampling technique was adopted for this research. This technique was adopted because of the peculiarity of this study A sample of one hundred and fifty was selected for the study of which one hundred and twenty-two returned the completed questionnaire representing a response rate of 81%. The study revealed that the most severe internal control problem in the building construction industry is lack of awareness of the environment, building construction firms adopt combination of two, three or all types of internal control system in their operations and It was also revealed that the control activities are not properly put in place in the operations of internal control system in building construction industry in the study area which renders the internal control system in the building construction industry in the study area ineffective, therefore the internal control system could not perform its functions like providing check and balances to prevent fraud, to check on the appropriateness of expenditures and to assess the effectiveness and the efficiency of the industry in the study area. It is recommended that there must be an increased awareness for the importance of internal control system in building construction industry in the study area and management must ensure that the organizational charts are updated and policies reviewed to ensure staff awareness of the control environment reduces the severity of problem of lack of awareness.