Longtime Riverside County Supervisor Roy Wilson announced Friday night that he was leaving office due to declining health.

Wilson, who has represented the 4th district on the Board of Supervisors since 1994, wrote in a letter to Riverside County residents that he was stepping down because of a sudden decline in health and need for treatment.

The news came unexpected, as Wilson was campaigning for his 2010 re-election.

The 74-year-old Wilson wrote in a letter: “My years as your supervisor have been wonderful years for me, both professionally and personally. I am grateful for the continuing support and trust that you, the voters, have given me all these years. I extend sincere thanks to my wife, family, friends and colleagues who have guided and supported my efforts for the 4th District. Especially, I thank my incredible staff. Their energy, commitment and competence have been the key to the success of my service to you.”

His 4th district is the largest geographic region in the country, covering 5,000 of Riverside’s 7,300 square miles. The area includes Blythe, Cathedral City, Coachella, Indian Wells, Indio, La Quinta, Palm Desert, Palm Spring and Rancho Mirage.

His replacement, who may be appointed by the Governor, will finish Wilson’s term through 2010.

Wilson recommended that Sen. John Benoit, R-Bermuda Dunes, fill his seat. Benoit told The Desert Sun newspaper that he is “definitely open” to the idea and that Wilson approached him about it last week.

Wilson championed environmental and public safety issues during his tenure on the board.

According to his bio on the Riverside County Web site, Wilson spent 33 years in higher education as an administrator and professor at California State University, Stanislaus and College of the Desert. During that time, his civic duties included serving as Planning Commissioner for the City of Palm Desert, and then as a member of the Palm Desert City Council for 17-and-half years. He also served four one-year terms as Mayor.

Wilson, who educated in journalism, was active in the professional journalism field as a member of several organizations.

James Spencer can be reached at jspencer@publicceo.com