Yes, according to the Census Bureau you are absolutely correct:By the time you add CR, Marion, Hiawatha, some of those surrounding towns, you’ll get there.
Hell, Marion is bigger than Carroll, Jefferson, and Boone combined.

Map of Iowa highlighting the Cedar Rapids Metropolitan Statistical Area.
The Cedar Rapids Metropolitan Statistical Area, as defined by the United States Census Bureau, is an area consisting of three counties in Iowa, anchored by the city of Cedar Rapids. As of the 2010 census, the MSA had a population of 257,940, and a 2013 population estimate of 262,421.
https://en.wikipedia.org/wiki/Cedar_Rapids,_Iowa_metropolitan_area