The Collaborative International Dictionary of English v.0.48:

Magistracy \Mag"is*tra*cy\, n.; pl. Magistracies. [From
   Magistrate.]
   1. The office or dignity of a magistrate. --Blackstone.
      [1913 Webster]

   2. The collective body of magistrates.
      [1913 Webster]

WordNet (r) 3.0 (2006):

magistracy
    n 1: the position of magistrate [syn: magistracy,
         magistrature]

Moby Thesaurus II by Grady Ward, 1.0:

125 Moby Thesaurus words for "magistracy":
   Kreis, aedileship, archbishopric, archdiocese, archiepiscopacy,
   archiepiscopate, aristocracy, arrondissement, bailiwick, bishopric,
   borough, canton, chairmanship, chancellery, chancellorate,
   chancellorship, chiefery, chiefry, chieftaincy, chieftainry,
   chieftainship, city, commune, congressional district,
   constablewick, consulate, consulship, county, deanery, departement,
   dictatorship, dictature, diocese, directorship, district, duchy,
   electoral district, electorate, emirate, episcopacy, government,
   governorship, hamlet, headship, hegemony, hierarchy, hundred,
   justiceship, leadership, lordship, magistrateship, magistrature,
   masterdom, mastership, mastery, mayoralty, mayorship, metropolis,
   metropolitan area, metropolitanate, metropolitanship, nobility,
   oblast, okrug, papacy, parish, pashadom, pashalic, patriarchate,
   patriarchy, pontificality, pontificate, popedom, popehood,
   popeship, precinct, prefectship, prefecture, premiership,
   presidency, presidentship, prime-ministership, prime-ministry,
   princedom, princeship, principality, proconsulate, proconsulship,
   protectorate, protectorship, province, provostry, provostship,
   rectorate, rectorship, regency, regentship, region, riding,
   ruling class, seigniory, seneschalship, seneschalsy, sheikhdom,
   sheriffalty, sheriffcy, sheriffdom, sheriffwick, shire, shrievalty,
   soke, stake, state, supervisorship, suzerainship, suzerainty,
   territory, town, township, tribunate, village, vizierate,
   viziership, wapentake, ward



Bouvier's Law Dictionary, Revised 6th Ed (1856):

MAGISTRACY, mun. law. In its most enlarged signification, this term includes
all officers, legislative, executive, and judicial. For example, in most of
the state constitutions will be found this provision; "the powers of the
government are divided into three distinct departments, and each of these is
confided to a separate magistracy, to wit: those which are legislative, to
one; those which are executive, to another; and those which are judiciary,
to another." In a more confined sense, it signifies the body of officers
whose duty it is to put the laws in force; as, judges, justices of the
peace, and the like. In a still narrower sense it is employed to designate
the body of justices of peace. It is also used for the office of a
magistrate.