Hello, Mom. Good question. There are many red or purple counties. However, Baltimore City, Montgomery County, and Prince George's County (my home) dominate in population and Dem registrations. MoCo and PG wrap around the east and north of DC and have many government employees and contractors as residents. Prince George's is the richest majority black county in perhaps the world. Much of that wealth comes from government contracts and quite a few government jobs.
The gerrymandering we talk about is why we have a single Republican in an 8 member Congressional delegation. With sensible districts we would probably have 3 now and might even have 4.
District 6.
An abomination.