How to merge self-created grids of areas and match it with county-level demographic information using tidycensus package in R

I have manually created grids of 20 mile radius each, across USA. Additionally I have also downloaded the demographic information at the county-level from US Census using tidycensus package in R. I want to map the demographic information at the county level to the manually created geographic grids, I am unable to do so. I understand that the grids might span several counties, in that case I want to use the demographic information from the county with the maximum intersection with the grid. I am looking for a direction to help me merge these two datasets together- the manually created grids and the county level demographic information.