There is no known documentation of Caroline's maiden surname. Family Search users have identified her as Caroline Wright. In the 1850 US Census (Union County, Georgia, household of W S Murray), there is an elderly woman named Sarah Wright. She could be Caroline's mother. No marriage record has been found for Winfield and Caroline Murray.
The fact of marriage has been inferred from the 1850 US Census, which appears to show a family group of husband, wife, and children, but does not actually state the relationship status for household members. Within the family, there is a photo of Jim Murray, the caption of which mentions Jim as the son of "Gains Murray Will's half-brother."
"United States Census, 1850," database with images, FamilySearch (https://familysearch.org/ark:/61903/1:1:MZY8-5CY : 12 April 2016), Caroline Murray in household of W S Murray, Union county, Union, Georgia, United States; citing family 748, NARA microfilm publication M432 (Washington, D.C.: National Archives and Records Administration, n.d.).