William Freame Johnston (29 November 1808 - 25 October 1872) was governor of Pennsylvania from 1848 to 1852. A lawyer by training, Johnston became district attorney of Westmoreland County at the age of 21 in 1829. He was elected to the Pennsylvania state legislature and switched from the Democratic Party to the Whig Party in 1847 to run for the Pennsylvania Senate.

He was named Senate Speaker in 1848 and, upon the resignation of Governor Francis Shunk, assumed the position of governor. Although, because of the transition, Shunk could have delayed the scheduled October elections, he chose to let them proceed and was narrowly elected to the position, defeating Democratic candidate Morris Longstreth by only 297 votes. Although he was part of the Free Soil faction of Whigs opposed to slavery, Johnston faced the federal Fugitive Slave Act and fought its enforcement in Pennsylvania. Johnston lost re-election to Democrat William Bigler in 1851.