A growing strand of empirical studies on mutual financial institutions have found that growth in membership increases ownership dispersion and hence membership apathy, allowing the board and professional managers to wield more power and control over the SACCO at the expense of the best interests of members who own the business. This gives rise to the agent-principal problem, potentially undermining the democratic and economic balance in the SACCO. This study proposed to examine this problem by investigating the influence of the size and outreach factors on agency-related costs (ARC) in the management of deposit-taking SACCOs in Kenya. Specifically, the value of asset, membership and peer group defined the size-related factors while the number of branch offices was used as the outreach factor. ARCs were measured as the ratio of the sum of directors’ expenses, staff emoluments and operating costs to the average assets. Data were obtained from 160 DT SACCOs in Kenya over the period 2014-2021 which represented 90.9 percent of licensed DT SACCOs. Both panel ordinary least squares and the 2-step generalized method of moments were utilized to address the objectives of the study. Descriptive as well as correlational analyses were also performed. The findings depict ARC levels within the global standard at 0.04 to 0.046 of the average assets. According to the results, smaller DT SACCOs seem to exhibit weaker expense efficiency compared to the larger ones. The results show a decline in expenditure by SACCOs post the COVID-19 period. In terms of peer grouping, the results reveal mixed influences in the case of large peer and small peer SACCOs in relation to ARCs, with some experiencing positive scale benefits and others experiencing scale disadvantages. However, the results show a consistent and significant inverse association between medium peer SACCOs and ARC. The results reveal that SACCOs with more members are associated with higher ARCs. In relation to outreach, the findings show that SACCOs with more branch offices have higher ARC. In relation to the control variables, it seems that the core capital ratio, asset quality and CEO gender are positively associated with ARC. The study calls for a cautious growth and expense management strategy by the DT SACCOs to assure solvency and self-sufficiency of the SACCOs in Kenya. Caution should also be exercised with branch expansion to avoid spiraling of SACCO expenses without commensurate returns, which might put the going concern status of the SACCO at risk. The study recommends that SACCOs need to improve their asset and expenditure management strategies as well as improve their member experience management which is important in reducing agency costs. Further, SACCOs should embrace technological and digital solutions to drive their outreach programs as an integral approach to reducing operational expenses. A critical issue for SACCOs is strategic cooperation to collectively invest in technology and other business infrastructure to leverage on economies of scale and scope as opposed to each SACCO invests individually thus driving the ARCs even higher.