- Beloit: A major community located in the southern portion of the county on the Illinois border. The city is home to Beloit College and is an industrial center.
- Clinton: A rural community located on the southern part of the county.
- Edgerton: A rural community in the northern portion of the county partially situated in Dane County.
- Evansville: A rural community in the northwestern part of the county.
- Janesville: The county seat and most populous city in the county. Janesville is the major economic hub of the region.
- Milton: A rural community located in the northern portion of the county. The city was home to the now defunct Milton College.
Rock County is one of the older counties in Wisconsin having developed around the Rock River, the region's first major economic driver. Beloit and Janesville, both located directly on the river, continue to be major regional economic centers and have the vast majority of shopping and entertainment in the county. Culturally, it is comparable to neighboring Winnebago County to the south.
Rock County is primarily accessible by Interstate 90 from either Rockford or Madison. A number of WI routes also service the County. Amtrak Thruway Motorcoach provides daily service to Janesville.
The following are the primary routes in and around the County:
- Interstate 90: The primary thoroughfare of the County, I-90 enters the County immediately east of Beloit and passes by Janesville and Edgerton before exiting the County.
- Interstate 43: Entering immediately north of Clinton, I-43 continues southeast and terminates at its junction with I-90 immediately east of Beloit.
- US 14: Entering immediately west of Darien, US 14 travels west through the County becoming a major thoroughfare in Janesville and passing through Evansville before exiting the County.
- WI 11: Another east-west thoroughfare, WI 11 enters the County concurrent with US 14 before splitting immediately east of Janesville. It travels with Business 14 through downtown Janesville before heading directly west and exiting the County immediately east of Broadhead.
- US 51: A major north-south route, US 51 enters the County near downtown Beloit before servicing Janesville and Edgerton.
- WI 26: Originating in downtown Janesville, WI 26 moves northeast passing through Milton before entering Jefferson County near Lake Koshkonong.