Question: Lockwood is a census-designated place in what county that is the most populous county in Montana?

Context paragraphs:
Lockwood, Montana: Lockwood is a census-designated place (CDP) in Yellowstone County, Montana, United States.  Lockwood had the largest growth rate in the state of Montana with 57.8% growth since 2000.  The 2010 census put Lockwood’s population at 6,797.  Lockwood is a suburb of Billings and is the second largest community in the Billings Metropolitan Area.  Annexation of Lockwood to Billings has been studied; however, the June 2009 Billings City Council Annexation Plan states that the city has no plans to annex Lockwood in the foreseeable future.

Stevensville, Maryland: Stevensville is a census-designated place (CDP) in Queen Anne's County, Maryland, and is the county's most populous place among both CDPs and municipalities.  The community is the eastern terminus of the Chesapeake Bay Bridge.  The Stevensville Historic District is one of only two registered historic districts in the county, the other being the Centreville Historic District.

Yellowstone County, Montana: Yellowstone County is the most populous county in the U.S. state of Montana.  As of the 2010 census, the population was 147,972, and a 2014 estimate put the population at 155,634.  Its county seat is Billings.  Yellowstone County is named for the Yellowstone River which roughly bisects the county from southwest to northeast.  The river in turn was named after the yellow Sandstone cliffs in what is now Yellowstone County.

Terrell County, Texas: Terrell County is a county located in the U.S. state of Texas.  As of the 2010 census, its population was 984, making it the eighth-least populous county in Texas, and the 37th-least populous county in the nation.  Its county seat is the census-designated place of Sanderson; there are no incorporated municipalities in the county.  The county was named for Alexander W. Terrell, a Texas state senator.

Germantown, Maryland: Germantown is an urbanized census-designated place in Montgomery County, Maryland.  With a population of 90,676 as of 2013 U.S. Census Bureau estimates, Germantown is the third most populous place in Maryland, after the city of Baltimore, and the census-designated place of Columbia.  If Germantown were to incorporate as a city, it would become the second largest incorporated city in Maryland, after Baltimore.  Germantown is located approximately 25-30 mi outside of the U.S. capital of Washington, D.C. and is an important part of the Washingtonian metropolitan area.

Cheektowaga (CDP), New York: Cheektowaga is a suburban community and census-designated place (CDP) in Erie County, New York, United States.  The population was 75,178 at the 2010 census, making it the most populous census-designated place in New York.  It is within the town of Cheektowaga.  The CDP includes Buffalo Niagara International Airport.

Lockwood, California: Lockwood is a census-designated place in Monterey County, California.  It is located 6 mi east-southeast of Jolon, 1.8 miles (2.9 km) north of the mouth of Tule Canyon, 3 miles (4.8 km) north of San Antonio River, and 9.3 miles (15 km) north of Bryson, at an elevation of 971 feet (296 m)

Malmstrom Air Force Base: Malmstrom Air Force Base is a United States Air Force base and census-designated place (CDP) in Great Falls, Cascade County, Montana, United States.  It was named in honor of World War II POW Colonel Einar Axel Malmstrom.  It is the home of the 341st Missile Wing (341 MW) of the Air Force Global Strike Command (AFGSC).  As a census-designated place, it had a population of 3,472 at the 2010 census.

Queen Anne's County, Maryland: Queen Anne's County is a county located in the U.S. state of Maryland.  As of the 2010 census, the population was 47,798.  Its county seat and most populous municipality is Centreville.  The census-designated place of Stevensville is the county's most populous place.  The county is named for Queen Anne of Great Britain who reigned when the county was established in 1706.

Montgomery County, Maryland: Montgomery County, officially the County of Montgomery, is a county in the U.S. state of Maryland.  As of the 2010 census, the population was 971,777, with a 2014 estimate putting the population at 1,030,447.  It is the most populous county in Maryland.  The county seat and largest municipality is Rockville, although the census-designated place of Germantown is the most populous place.

Supporting paragraphs: Lockwood, Montana Yellowstone County, Montana
Answer: Yellowstone County