Lyndon Earl "Mike" Welday (December 13, 1878 in Conway, Iowa, United States – May 28, 1942 in Leavenworth, Kansas, USA) was a left-handed Major League Baseball outfielder who played for the Chicago White Sox in 1907 and 1909. Overall, he hit .202 in 53 major league games, collecting 22 hits in 109 at-bats. He had five runs, five RBI and two stolen bases. In the field, he committed six errors in 39 games for a .900 fielding percentage. Following his death, he was interred at in Lansing, Kansas.