Generally, the small counties in Maryland are pretty strongly Republican. The medium-sized counties (Anne Arundel, Howard, Charles) are swing counties. The largest counties (except for Baltimore County, a swing county) are heavily Democratic.
All states have some mix of Democratic and Republican voters. But the mix in MD tilts strongly toward the Dems. It is clearly one of the most Democratic states in the country. The state legislature is almost 3/4 Dem in both houses, largely due to the fact that every single legislator in Montgomery, PG, and Baltimore City are Democrats. These legislators alone are almost enough to constitute a majority (22 out of 47 state senate seats).
There was a time when Baltimore City alone held a majority of the population of Maryland.