Mesoscale Convective Systems (MCS), a type of organized convective storms that often produce extreme precipitation and flooding, contribute to 30-70% of warm-season precipitation in the central U.S. While extreme precipitation has been found to increase with a warming climate, how the scaling depends on different precipitation regimes is not well understood. In this study, we examine long-term changes of precipitation in the central U.S. associated with changes of MCSs. A 35-year MCS database has been constructed based on North American Land Data Assimilation System (NLDAS) observed precipitation and validated against a shorter satellite-based record. We find that the increase in total precipitation in the central U.S. (11%/decade) is due to increasing duration and frequency of MCSs, resulting in an increase of MCS precipitation (27%/decade), while non-MCS precipitation decreases (5%/decade). Changes in the large-scale environments responsible for the increasing longevity of MCSs in both reanalysis and numerical model experiments are analyzed to better understand the underlying mechanisms, with implications for potential future changes in a warming climate.