To answer this question, a paper by Kimmey et al. (2021) use data from the AHRQ Compendium of US Health Systems to answer this question. They find physicians are increasingly becoming part of larger health systems.
The average change in the share of physicians in systems across MSAs from 2016 to2018 was 8.8 percentage points at the MSA level; the median change was 7.4 percentage points (data not shown). These figures are less than the national change in the share of physicians in systems from 2016 to 2018 (11 percentage points), in part because many of the largest MSAs had a change that was larger than 8.8 percentage points
The authors note that consolidation occurs most frequently in the Northeast and Midwest.